JP2004070092A - Zoom photography optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a wide power variation range from power smaller than the power of an objective to the power exceeding ten times. <P>SOLUTION: An optical system which has at least a 1st positive lens group, a 2nd negative lens group, and a 3rd positive lens group in order from the objective side, moves the 2nd lens group and 3rd lens group for power variation from a low-power end to a high-power end so that the gap between the 1st and 2nd lens groups is shorter at the high-power end than at the low-power end and the gap between the 2nd and 3rd lens groups is longer at the high-power end than at the low-power end, and forms an intermediate image between the 1st and 2nd lens groups at the low-power end, satisfies conditions of (1) 1≤FH/FL≤3 and (2) 3≤MGH/MGL≤20. <P>COPYRIGHT: (C)2004,JPO

Description

つまり、ズーム撮影光学系の変倍比Ｚは条件（１）と条件（２）の積にて表すことができる。
【００２５】
本発明のズーム撮影光学系は、前記のように、対物レンズ側より順に、正の屈折力の第１レンズ群と、負の屈折力よりなる第２レンズ群と、正の屈折力の第３レンズ群を少なくとも有している。このような本発明のズーム撮影光学系において、第３レンズ群より像側に更にレンズ群を配置する場合、次に示すような構成の光学系が望ましい。
【００２６】
第３レンズ群に続いて一つのレンズ群を配置する場合、正の屈折力の第４レンズ群を配置することが望ましい。そして低倍端から高倍端への変倍に際して、第３レンズ群と第４レンズ群の間隔がはじめは長くなり、途中から短くなるようにするように構成することが望ましい。
【００２７】
即ち、本発明のズーム撮影光学系を四つのレンズ群にて構成する場合、対物レンズ側から、正の屈折力の第１レンズ群、負の屈折力の第２レンズ群、正の屈折力の第３レンズ群及び正の屈折力の第４レンズ群の順に配置する。そして、低倍端から高倍端での変倍に際し第１レンズ群と第２レンズ群の間隔が短くなり、第３レンズ群と第４レンズ群の間隔がはじめ長くなってから短くなるように、第２、第３、第４レンズ群が夫々光軸に沿って移動するように構成する。そして、低倍端において第１レンズ群と第２レンズ群との間に中間像が形成されるようにし、前記の条件（１）、（２）を満足する。
【００２８】
また、第３レンズ群に続いて一つのレンズ群を配置する場合、他の構成として負の屈折力の第４レンズ群を配置しても良い。そして低倍端から高倍端への変倍に際して、第３レンズ群と第４レンズ群との間隔が長くなることが望ましい。
【００２９】
即ち、本発明のズーム光学系を四つのレンズ群にて構成する場合、対物レンズ側から、正の屈折力の第１レンズ群、負の屈折力の第２レンズ群、正の屈折力の第３レンズ群及び負の屈折力の第４レンズ群の順に配置する。そして、低倍端から高倍端の変倍に際し、第１レンズ群と第２レンズ群の間隔がはじめ長くなってから短くなり、第２レンズ群と第３レンズ群の間隔がはじめ短くなってから長くなり、第３レンズ群と第４レンズ群の間隔が長くなるように、第２、第３、第４レンズ群が夫々光軸に沿って移動するように構成する。そして、低倍端において第１レンズ群と第２レンズ群との間に中間像が形成されるようにし、前記の条件（１）、（２）を満足する。
【００３０】
又、本発明のズーム撮影光学系において、第３レンズ群に続いて二つのレンズ群を配置する場合、第３レンズ群から順に正の屈折力の第４レンズ群と、正の屈折力又は負の屈折力の第５レンズ群を配置した構成が好ましい。そして、低倍端から高倍端への変倍に際して、追加配置したレンズ群は、第３レンズ群と第４レンズ群の間隔がはじめ長くなってから短くなり、第４レンズ群と第５レンズ群の間隔が長くなるように移動することが望ましい。
【００３１】
即ち、本発明のズーム撮影光学系を五つのレンズ群で構成する場合、対物レンズ側から、正の屈折力の第１レンズ群、負の屈折力の第２レンズ群、正の屈折力の第３レンズ群、正の屈折力の第４レンズ群及び正の屈折力を有する第５レンズ群の順に配置する。そして、低倍端から高倍端への変倍に際し、第１レンズ群と第２レンズ群の間隔が短くなり、第２レンズ群と第３レンズ群の間隔が長くなり、第３レンズ群と第４レンズ群の間隔がはじめ長くなってから短くなり、第４レンズ群と第５レンズ群の間隔が長くなるように、第２、第３、第４レンズ群を夫々光軸に沿って移動するように構成する。そして、第１レンズ群と第２レンズ群の間に中間像が形成されるようにし、前記条件（１）、（２）を満足する。
【００３２】
また、本発明のズーム光学系を五つのレンズ群で構成する他の例では、対物レンズ側から、正の屈折力の第１レンズ群、負の屈折力の第２レンズ群、正の屈折力を有する第３レンズ群、正の屈折力を有する第４レンズ群及び負の屈折力の第５レンズ群の順に配置する。そして、低倍端から高倍端への変倍に際し、第１レンズ群と第２レンズ群の間隔が短くなり、第２レンズ群と第３レンズ群の間隔が長くなり、第３レンズ群と第４レンズ群の間隔がはじめ長くなってから短くなり、第４レンズ群と第５レンズ群の間隔が長くなるように、第２、第３、第４レンズ群を夫々光軸に沿って移動させるように構成する。そして、低倍端で第１レンズ群と第２レンズ群の間に中間像が形成されるようにし、前記条件（１）、（２）を満足する。
【００３３】
また、上記の各構成における本発明のズーム撮影光学系は、下記条件（３）、（４）、（５）を満足することが望ましい。
（３）　　０．３＜Ｄ１／Ｄ０＜０．７
（４）　　０．１５＜Ｄ２／Ｄ０＜０．７
（５）　　０＜ＦＢ／Ｄ０＜０．３
ただし、
Ｄ０は第１レンズ群における対物レンズに最も近いレンズ面から最終像位置までの距離、
Ｄ１は第１レンズ群における対物レンズに最も近いレンズ面から中間像位置までの低倍端における距離、
Ｄ２は低倍端から高倍端へ変倍したときの第２レンズ群の移動量、
ＦＢは最終像に最も近い位置にあるレンズの最終像側のレンズ面から最終像までの距離である。
【００３４】
本発明のズーム撮影光学系において、条件（３）を満足すれば、低倍端での軸外収差と高倍端での球面収差を良好に補正できる。また条件（４）を満足することにより、高い変倍比になし得る。また条件（５）を満足することにより、ズーム撮影光学系のバックフォーカスを適切なものにし、コンパクトな構成にすることが可能となる。
【００３５】
条件（３）において、Ｄ１／Ｄ０の値が下限値の０．３よりも小になると、第１レンズ群から中間像位置までの距離が短くなって第１レンズ群の屈折力が強くなる。このとき低倍端の軸外主光線は第２レンズ群に入射する際に、光線高が高くなり、入射角度が大きくなってしまう。従って低倍端での軸外収差と、瞳収差も悪化するので好ましくない。また上限値の０．７より大になると第１レンズ群のパワーが弱くなり、中間像位置から最終像位置までの間隔が短くなりすぎる。そのため、三つのレンズ群よりなる撮影光学系の場合、第２レンズ群、第３レンズ群の移動スペースが小になる。また四つまたは五つのレンズ群よりなる撮影光学系の場合は、第２レンズ群、第３レンズ群、第４レンズ群の移動スペースが短くなる。この結果、いずれの場合も高い変倍比を得ることができなくなる。
【００３６】
条件（４）において、Ｄ２／Ｄ０の値が下限値の０．１５よりも小になると、第２レンズ群の負のパワーが強くなりすぎる。この結果、低倍端で非点収差とコマ収差が悪化し、高倍端では球面収差が悪化する。また条件（４）の上限値０．７より大になると、第２レンズ群の負のパワーが弱くなる。この結果、高い変倍比を得ることができない。また、第３レンズ群あるいは第３レンズ群と第４レンズ群の移動量が小さくなり、像面位置を一定にすることが困難になる。
【００３７】
条件（５）において、ＦＢ／Ｄ０が下限値０よりも小になると、最終像が最終レンズ群に近い位置に形成される。そのため、撮影装置を配置しようとすると、最終レンズ群との間で構造的な干渉が起こる。条件（５）において、ＦＢ／Ｄ０が上限値の０．３よりも大になると、第１レンズ群から最終レンズ群までの間隔が短くなる。この結果、高い変倍比を得ることが困難になる。
【００３８】
上記の各構成における本発明のズーム撮影光学系では、中間像と最終像との間に対物レンズの瞳と共役な像（瞳共役像）が形成されるようにするのが良い。この時、瞳共役像の位置あるいはその近傍に開口絞りを配置し、変倍に応じて開口絞りが光軸上を移動するのが好ましい。また、開口絞りの位置を固定する場合は、この開口絞りの径を変化させるのが良い。このようにすれば、対物レンズを通過する光束の径を変化させることができる。
【００３９】
前記のように、瞳共役位置あるいはその近傍に開口絞りを配置し、開口絞り径を変化させることができるようにすると、低倍端での開口数を制限して周辺での光量の減少やけられを抑えることができる。しかも、軸外収差性能を向上させることができる。また、低倍での観察や撮影時には、解像力よりも周辺での光量を確保することや、けられを少なくする等を優先させるほうが好ましい場合がある。このような点からも、上記構成は有効である。また、変倍に応じて、開口絞りの径を変化させることにより、最終像面側の射出側開口数を一定にすることができる。これにより、変倍の際に像の明るさを一定にすることが可能になる。
【００４０】
一方、高倍端では、解像力が必要なため開口数を制限しないことが望まれる。ただし、開口絞りを絞ることで、焦点深度を深くして観察する場合もある。そのため、開口絞りの径を変化できるようにしておくのが好ましい。
【００４１】
また、変倍に関係なくこの開口絞りの位置を光路中に固定させるためには、開口絞りを第３レンズ群から最終レンズ群までの間に配置するのが好ましい。その場合、すべての倍率において射出瞳位置が一定になる。
【００４２】
あるいは、中間像位置から最終像位置の間に、開口絞りを複数箇所設けるようにすることもできる。夫々の変倍での状態の瞳共役位置近傍に配置された開口絞り径を適切に絞り、それ以外の開口絞り径を開放する。これによって、瞳共役位置が光軸上を移動した場合でも、複数の開口絞り径を適切な径にすることで、対物レンズの開口を制限することができるので好ましい構成となる。
【００４３】
また、前述の本発明のズーム撮影光学系において、第１レンズ群を複数のレンズ成分にて構成し、しかも正レンズと負レンズよりなる接合レンズを少なくとも含むようにするのが良い。また最終レンズ群を複数のレンズ群にて構成し、そのうち中間像側に凹面を向けた負の屈折力のレンズを含むようにするのが望ましい。
【００４４】
また上記構成で、下記条件（６）、（７）を満足するのが好ましい。
（６）　　νＰ−νＮ≧３０
（７）　　Ｇｎ≧１．６
ただし、
νＰは第１レンズ群中の接合レンズの正レンズのアッベ数、
νＮは第１レンズ群中の接合レンズの負レンズのアッベ数、
Ｇｎは前記中間像側に凹面を向けた負の屈折力のレンズの屈折率である。
【００４５】
条件（６）を満足すると、高倍端での球面収差と低倍端での倍率の色収差を良好に補正し得る。条件（６）において、νＰ−νＮの値が下限値の３０より小になると、高倍端における球面収差と低倍端における倍率の色収差の補正が困難になる。
【００４６】
また、条件（７）を満足すると、ペッツバール和を小さくして像面湾曲を補正することができる。また、ズーム全域でのコマ収差と非点収差を良好に補正することが可能になる。条件（７）において、Ｇｎの下限値が１．６よりも小になると、中間像側に凹面を向けた負の屈折力をもつレンズの曲率半径が小になる。そのため、ズーム全域でのコマ収差と非点収差を良好に補正することが困難になる。
【００４７】
ズーム撮影光学系は、各レンズ群で収差を補正するために、単レンズではなく接合レンズにて構成することが好ましい。このようにすればズーム全域での収差を良好に補正することができる。
【００４８】
本発明のズーム撮影光学系において、第１レンズ群を二つの正の屈折力のレンズ成分（前群と後群）にて構成し、両レンズ成分の間隔（前群と後群の間隔）Ｄ１１が下記条件（８）を満足することが望ましい。
（８）　　０．３＜Ｄ１１／Ｄ１＜０．８
ただし、Ｄ１１は前記前群と後群の間隔である。
【００４９】
上記条件（８）を満足すると、低倍端での倍率の色収差と高倍端での球面収差の補正が容易になる。また第１レンズ群の主点位置が中間像側に移動するので、第２レンズ群の負屈折力が強くなる。その結果、第２レンズ群の移動量が小さくなるのでレイアウト上好ましい構成となる。また、低倍端での倍率の色収差と、高倍端での球面収差の補正が容易になる。
【００５０】
条件（８）において、Ｄ１１／Ｄ１の値が下限値の０．３よりも小になると第１レンズ群の主点位置の移動量が少なくなるので、第２レンズ群の負の屈折力を強くできない。そのため、変倍の際に第２レンズ群の移動量を大きくとらねばならず、光学系が大型化する。また、上限値の０．８より大になると、第１レンズ群の後群から中間像までの間隔が短くなりすぎる。そのため、第１レンズ群の後群で、低倍端における軸外主光線高と高倍端の軸上光線高が小になる。その結果、収差補正のための効果が得られない。また第２レンズ群の変倍時の移動量が少なく、光学系の変倍比を大きくすることができない。
【００５１】
本発明のズーム撮像光学系の実施例を以下に示す。本発明の第１実施例乃至第７の実施例は、夫々図１乃至図７にて示す通りの構成であって、次の表１乃至表７に示すデータを有する。
【００５２】

【００５３】

【００５４】

【００５５】

【００５６】

【００５７】

【００５８】

上記データにおいて、面番号１、２、・・・は夫々対物レンズ側から順にズーム撮影光学系の各面を表わし、各面番号に対応する曲率半径、間隔が図１乃至図７におけるｒ１、ｄ１等に対応し、屈折率Ｎｄ、Ｖｄは該当する面と次の面との間の媒質のｄ線に対する屈折率、アッベ数を示している。またデータ中のａ１，ａ２，ａ３，ａ４は夫々変倍時の可変間隔である。実施例１、２、３、及び７では、焦点距離が４５ｍｍ、１８０ｍｍ、９００ｍｍの時の可変間隔の値である。また、実施例４、５、６では、焦点距離が４５ｍｍ、１４４ｍｍ、３６０ｍｍの時の可変間隔の値である。また、曲率半径、間隔、焦点距離、開口絞り径、射出瞳位置、像高等の長さの単位はｍｍである。また射出瞳位置は最終面からの距離（ｍｍ）である。
【００５９】
第１の実施例は、図１に示す通りで、対物レンズの後方より順に、正の屈折力の第１レンズ群Ｇ１と負の屈折力の第２レンズ群Ｇ２と正の屈折力の第３レンズ群Ｇ３と正の屈折力の第４レンズ群Ｇ４と正の屈折力の第５レンズ群Ｇ５とより構成されている。そして、低倍端から高倍端へ変倍を行なう際に、第２レンズ群Ｇ２、第３レンズ群Ｇ３、第４レンズ群Ｇ４が光軸に沿って移動する。この時、第１レンズ群Ｇ１と第２レンズ群Ｇ２の間隔が短くなり、第２レンズ群Ｇ２と第３レンズ群Ｇ３との間隔が長くなり、第３レンズ群Ｇ３と第４レンズ群Ｇ４との間隔がいったん長くなり後に短くなり、第４レンズ群Ｇ４と第５レンズ群Ｇ５との間隔が長くなる。
【００６０】
この第１の実施例では、第１レンズ群Ｇ１は、凸レンズと凹レンズを接合した接合正レンズの前群Ｇ１Ｆと、凸レンズの後群Ｇ１Ｒとにて構成されている。第２レンズ群Ｇ２は、負のメニスカスレンズと正のメニスカスレンズとを接合した負の接合メニスカスレンズにて構成されている。第３レンズ群Ｇ３は、負のメニスカスレンズと正のメニスカスレンズとを接合した正の接合レンズにて構成されている。第４レンズ群Ｇ４は、負のメニスカスレンズと正のメニスカスレンズとを接合した正の接合メニスカスレンズと、凸レンズとにて構成されている。そして、第５レンズ群Ｇ５は、両凹レンズと正のメニスカスレンズを接合した負の接合レンズと、両凹レンズと両凸レンズとを接合した負の接合メニスカスレンズと、凸レンズとにて構成されている。
【００６１】
この第１の実施例、第３レンズ群Ｇ３と第４レンズ群Ｇ４の間に、対物レンズの瞳位置と共役な位置がある。そして、この瞳共役位置の近傍に、開口絞りＳが配置されている。また、開口絞りＳは、変倍時に第４レンズ群Ｇ４と一体に光軸上を移動する。
【００６２】
前述のように、第１の実施例では、図１の（Ａ）低倍端、（Ｂ）中間倍率、（Ｃ）高倍端に示すように、第２レンズ群Ｇ２、第３レンズ群Ｇ３、第４レンズ群Ｇ４を移動させている。これによって、焦点距離が４５ｍｍ（低倍端）から１８０ｍｍ（中間倍率）、更に９００ｍｍ（高倍端）まで変化する。なお、焦点距離４５ｍｍの時の視野数が８であり、それ以外の焦点距離では視野数が１１である。
【００６３】
また、焦点距離が４５ｍｍから１８０ｍｍまでは、射出側開口数が０．０３２になるように開口絞りＳの径を設定してある。そして、焦点距離１８０ｍｍから９００ｍｍまでは、開口絞りＳは開放になっている。これにより、対物レンズの瞳径１７．０９ｍｍを、開口絞りＳにより制限しないように構成されている。この結果、低倍端では像面の明るさが一定に保たれ、周辺での光量の減少を抑えることができる。
【００６４】
この第１の実施例は第３レンズ群Ｇ３の移動量が少ないため、像面Ｉにおける主光線の入射角が変倍中のどの状態でも約２度以内に抑えられている。すなわち、ＣＣＤ素子に特有の現象である色シェーディングを抑える上で有効な構成になっている。
【００６５】
この第１の実施例は、低倍端において、第１レンズ群Ｇ１と第２レンズ群Ｇ２の間に、中間像ＩＭが形成されるように構成されている。中間倍率と高倍端とにおいては、第２レンズ群Ｇ２が低倍端の中間像の位置ＩＭよりも第１レンズ群Ｇ１側に移動する。その結果、中間倍率と高倍端での中間像位置［図１の（Ｂ）、（Ｃ）におけるＩＭ］は像側に移動している。
【００６６】
また、低倍端では、図１（Ａ）に示すように、第２レンズ群Ｇ２から第５レンズ群Ｇ５で、中間像ＩＭを像面Ｉにリレーしている。そして、主点位置を像側にシフトさせるために、中間像ＩＭと第２レンズ群Ｇ２の間隔を大にし、第２レンズ群Ｇ２から第５レンズ群Ｇ５までの間隔を小にしている。このように、第２レンズ群Ｇ２から第５レンズ群Ｇ５を像面側に配置することにより、縮小倍率になるようにしている。
【００６７】
また、図１（Ｂ）に示す中間倍率においては、第３レンズ群Ｇ３から第５レンズ群Ｇ５で、中間像ＩＭを像面Ｉにリレーしている。そして、第３レンズ群Ｇ３は、中間像に対してフィールドレンズの働きをしている。すなわち、軸外光束のけられをなくし、軸外収差を補正する作用をする。また、第４レンズ群Ｇ４は、低倍端の位置よりも第３レンズ群Ｇ３側へ移動して、中間像ＩＨから像面Ｉまでの倍率を大きくしている。
【００６８】
更に、高倍端では図１（Ｃ）のように、第３レンズ群Ｇ３から第５レンズ群Ｇ５までの光学系により、中間像ＩＭを像面までリレーする。また、第３レンズ群Ｇ３と第４レンズ群Ｇ４を中間像側に移動させている。これにより、リレー光学系の主点位置を中間像側に移動させ、拡大倍率を実現している。
【００６９】
この第１の実施例は、前記条件（１）乃至条件（７）を満足する。
【００７０】
この第１の実施例では対物レンズの構成は記載していないが、対物レンズの瞳径は１７．０９ｍであり、対物レンズの瞳位置から第１レンズ群Ｇ１までの距離は１６９ｍｍである。
【００７１】
この第１の実施例の収差状況は、夫々図８（焦点距離４５ｍｍ時）、図９（焦点距離１８０ｍｍ時）、図１０（焦点距離９００ｍｍ時）に示す通りである。
【００７２】
本発明の第２の実施例は、図２に示すとおりで、対物レンズの後方から順に、正の屈折力をもつ第１レンズ群Ｇ１と、負の屈折力をもつ第２レンズ群Ｇ２と、正の屈折力をもつ第３レンズ群Ｇ３と、正の屈折力をもつ第４レンズ群Ｇ４と正の屈折力をもつ第５レンズ群Ｇ５とより構成されている。そして、低倍端から高倍端への変倍に際して、第２レンズ群Ｇ２、第３レンズ群Ｇ３、第４レンズ群Ｇ４が光軸に沿って移動する。この時、第１レンズ群Ｇ１と第２レンズ群Ｇ２の間隔が短くなり、第２レンズ群Ｇ２と第３レンズ群Ｇ３との間隔が長くなり、第３レンズ群Ｇ３と第４レンズ群Ｇ４との間隔がいったん長くなり後に短くなり、第４レンズ群Ｇ４と第５レンズ群Ｇ５の間隔が長くなる。
【００７３】
この第２の実施例では、第１レンズ群Ｇ１は、凹レンズと凸レンズを接合したパワーの弱い負の接合レンズの前群Ｇ１Ｆと、凸レンズの後群Ｇ１Ｒとで構成されている。第２レンズ群Ｇ２は、負のメニスカスレンズと正のメニスカスレンズとを接合した負の接合メニスカスレンズにて構成されている。第３レンズ群Ｇ３は、負のメニスカスレンズと凸レンズとを接合した正の接合レンズにて構成されている。第４レンズ群Ｇ４は、凸レンズと、負のメニスカスレンズと凸レンズとを接合した正の接合レンズとにて構成されている。そして、第５レンズ群Ｇ５は、両凹レンズと正のメニスカスレンズとを接合した負の接合レンズと、両凹レンズと凸レンズとを接合した正の接合メニスカスレンズと、正のメニスカスレンズとにて構成されている。
【００７４】
この第２の実施例は、第３レンズ群Ｇ３と第４レンズ群Ｇ４の間に、対物レンズの瞳位置と共役な位置がある。そして、この瞳共役位置の近傍に、開口絞りＳが配置されている。また、開口絞りＳは、変倍時に第４レンズ群Ｇ４と一体に光軸上を移動する。
【００７５】
前述のように、第２の実施例では、図２の（Ａ）低倍端、（Ｂ）中間倍率、（Ｃ）高倍端に示すように、第２レンズ群Ｇ２、第３レンズ群Ｇ３、第４レンズ群Ｇ４を移動させている。この変倍によって、焦点距離が４５ｍｍ（低倍端）から１８０ｍｍ（中間倍率）、更に９００ｍｍ（高倍端）まで変化する。なお、焦点距離４５ｍｍの時の視野数が８であり、それ以外の焦点距離では視野数が１１である。
【００７６】
また、焦点距離が４５ｍｍから１８０ｍｍまでは、射出側開口数が０．０３２となるように開口絞りＳの径を設定してある。また、焦点距離が１８０ｍｍから９００ｍｍまでは、開口絞りＳを開放としている。これにより、対物レンズの瞳径１７．０９ｍｍを、開口絞りＳにより制限しない構成にしている。この結果、低倍端では像面の明るさが一定に保たれ、周辺での光量の減少を抑えることができる。
【００７７】
この第２の実施例は第３レンズ群Ｇ３の移動量が少ないため、像面Ｉでの主光線の入射角度は変倍のどの状態でも２度内に抑えられている。すなわち、ＣＣＤ素子に特有の現象である色シェーディングを抑える上で有効な構成になっている。
【００７８】
この第２の実施例も条件（１）乃至条件（７）を満足している。また、各レンズ群の作用は、第１の実施例と同様である。
【００７９】
この第２の実施例でも対物レンズの構成は記載していないが、対物レンズの瞳径は１７．０９ｍであり、対物レンズの瞳位置から第１レンズ群Ｇ１までの距離は１７１ｍｍである。
【００８０】
この第２の実施例の収差状況は、夫々図１１（焦点距離４５ｍｍ時）、図１２（焦点距離１８０ｍｍ時）、図１３（焦点距離９００ｍｍ時）に示す通りである。
【００８１】
本発明の第３の実施例は、図３に示す通りで、対物レンズの後方から順に、正の屈折力の第１レンズ群Ｇ１と、負の屈折力の第２レンズ群Ｇ２と、正の屈折力の第３レンズ群Ｇ３と、正の屈折力の第４レンズ群Ｇ４と正の屈折力の第５レンズ群Ｇ５とにて構成されている。そして、低倍端から高倍端への変倍に際して、第２レンズ群Ｇ２、第３レンズ群Ｇ３、第４レンズ群Ｇ４が夫々光軸上を移動する。この時、第１レンズ群Ｇ１と第２レンズ群Ｇ２の間隔が短くなり、第２レンズ群Ｇ２と第３レンズ群Ｇ３との間隔がいったん短くなり後に長くなり、第３レンズ群Ｇ３と第４レンズ群Ｇ４の間隔がいったん長くなり後に短くなり、第４レンズ群Ｇ４と第５レンズ群Ｇ５の間隔が長くなる。
【００８２】
また、この第３の実施例では、第１レンズ群Ｇ１は、凸レンズと、凸レンズと凹レンズとを接合したパワーの弱い正の接合レンズよりなる前群Ｇ１Ｆと、正レンズよりなる後群Ｇ１Ｒとにて構成されている。第２レンズ群Ｇ２は、負のメニスカスレンズと正のメニスカスレンズとを接合した負の接合レンズにて構成されている。第３レンズ群Ｇ３は、負のメニスカスレンズと凸レンズとを接合した正の接合レンズにて構成されている。第４レンズ群Ｇ４は、正のメニスカスレンズと、負のメニスカスレンズと凸レンズとを接合した正の接合レンズとにて構成されている。第５レンズ群Ｇ５は、第４レンズ群Ｇ４側にゆるい凸面を向けた負のメニスカスレンズと、両凹レンズと正レンズとを接合した負の接合メニスカスレンズと、正のメニスカスレンズにて構成されている。
【００８３】
また、この第３の実施例は、第３レンズ群Ｇ３と第４レンズ群Ｇ４の間に、対物レンズの瞳位置と共役な位置がある。そしてこの瞳共役位置の近傍に、開口絞りＳが配置されている。また、開口絞りＳは、変倍時に第４レンズ群Ｇ４と一体になって光軸上を移動する。
【００８４】
前述のように、第３の実施例では、図３の（Ａ）低倍端、（Ｂ）中間倍率、（Ｃ）高倍端に示すように、第２レンズ群Ｇ２、第３レンズ群Ｇ３、第４レンズ群Ｇ４を移動させている。この変倍によって、焦点距離が４５ｍｍ（低倍端）から１８０ｍｍ（中間倍率）、更に９００ｍｍ（高倍端）まで変化する。なお、焦点距離４５ｍｍの時の視野数が８であり、それ以外の焦点距離では視野数が１１である。
【００８５】
また、焦点距離が４５ｍｍから１８０ｍｍまでは、射出側開口数が０．０３２になるように開口絞りＳの径を設定してある。また、焦点距離が１８０ｍｍから９００ｍｍまでは開口絞りＳを開放にしている。これにより、対物レンズの瞳径の１７．０９ｍｍを、開放絞りＳにより制限しないように構成している。この結果、低倍端では像面の明るさが一定に保たれ、周辺での光量の減少を抑えることができる。
【００８６】
この第３の実施例は第３レンズ群Ｇ３の移動量が少いため、像面Ｉでの主光線の入射角度は、変倍のどの状態でも約２度以内に抑えられている。すなわち、ＣＣＤ素子に特有の現象である色シェーディングを抑える上で有効な構成になっている。
【００８７】
この第３の実施例は、条件（１）乃至条件（８）を満足する。また、各レンズ群の作用は、第１の実施例と同様である。
【００８８】
第３の実施例は、第１レンズ群Ｇ１が前群Ｇ１Ｆと後群Ｇ１Ｒにて構成され、また第２レンズ群Ｇ２の移動量が小で、レイアウト上好ましい。また、対物レンズの構成は示していないが、対物レンズの瞳径は１７．０９ｍｍであり、対物レンズの瞳位置から第１レンズ群Ｇ１までの距離は１７１ｍｍである。
【００８９】
この第３の実施例の収差状況は、夫々図１４（焦点距離４５ｍｍ時）、図１５（焦点距離１８０ｍｍ時）、図１６（焦点距離９００ｍｍ時）に示す通りである。
【００９０】
本発明の第４の実施例は、図４に示す通りの構成である。即ち、対物レンズの後方から順に、正の屈折力の第１レンズ群Ｇ１と、負の屈折力の第２レンズ群Ｇ２と、正の屈折力の第３レンズ群Ｇ３とより構成されている。そして、低倍端から高倍端への変倍に際して、第２レンズ群Ｇ２と第３レンズ群Ｇ３とが光軸に沿って移動する。この時、第１レンズ群Ｇ１と第２レンズ群Ｇ２との間隔が短くなり、第２レンズ群Ｇ２と第３レンズ群Ｇ３との間隔が長くなる。
【００９１】
また、この第４の実施例では、第１レンズ群Ｇ１が凸レンズと、凸レンズと凹レンズとを接合したパワーの弱い接合レンズとにて構成される前群Ｇ１Ｆと、正レンズにて構成される後群Ｇ１Ｒとよりなる。第２レンズ群Ｇ２は、負のメニスカスレンズと正のメニスカスレンズとを接合した接合負メニスカスレンズにて構成されている。更に、第３レンズ群Ｇ３は、負のメニスカスレンズと凸レンズとを接合した接合正レンズと、正レンズと、像面側に強い凹面を向けた負メニスカスレンズと、第２レンズ群Ｇ２に凹面を向けた両凹レンズと両凸レンズとを接合した接合負レンズと、正のメニスカスレンズとにて構成されている。
【００９２】
この第４の実施例の光学系中に、二つの開口絞りＳ１（第９面）、Ｓ２（第２５面）を配置する。低倍端では対物レンズの瞳共役位置が第２レンズ群Ｇ２の近傍にあるので、開口絞りＳ１を第２レンズ群近傍に配置する。また中間倍率では、対物レンズの瞳共役位置が、第３レンズ群Ｇ３近傍にあるので、開口絞りＳ２を第３レンズ群Ｇ３内に配置する。つまり低倍端では、対物レンズの開口を制限するように開口絞りＳ１の径を絞り、開口絞りＳ２の径を開放にする。また中間倍率では、開口絞りＳ１の径を開放にし、対物レンズの開口を制限するように開口絞りＳ２の径を制限する。高倍端では、開口絞りＳ１、Ｓ２の径を開放する。
【００９３】
前述のように、第４の実施例では、図４の（Ａ）低倍端、（Ｂ）中間倍率、（Ｃ）高倍端に示すように、第２レンズ群Ｇ２、第３レンズ群Ｇ３を移動させている。この変倍によって、焦点距離が４５ｍｍ（低倍端）から１４４ｍｍ（中間倍率）、更に３６０ｍｍ（高倍端）まで変化する。なお、焦点距離４５ｍｍの時の視野数が８であり、それ以外の焦点距離では視野数が１１である。
【００９４】
また、焦点距離が４５ｍｍから１４４ｍｍまでは、射出側開口数が０．０３となるように開口絞りＳ１、Ｓ２の径を設定してある。また、焦点距離が１４４ｍｍから３６０ｍｍまでは、開口絞りＳ１、Ｓ２を開放としている。これにより、対物レンズの瞳径１４．４ｍｍを、開口絞りＳ１、Ｓ２によって制限しない構成にしている。この結果、低倍端では像面の明るさが一定に保たれ、周辺での光量の減少を抑えることができる。
【００９５】
また、第４の実施例では、三つのレンズ群よりなる少ないレンズ群にて構成されているにも拘らず、条件（１）乃至条件（６）を満足している。これにより、高い変倍比で優れた収差性能のズーム光学系を実現した。
【００９６】
また、第４の実施例の光学系は、更に条件（８）を満足している。これにより、第２レンズ群Ｇ２の移動量を少なくすることができるので、レイアウト上も好ましい構成である。
【００９７】
この第４の実施例でも対物レンズの構成は記載していないが、対物レンズの瞳径は１４．４ｍｍであり、対物レンズの瞳位置から第１レンズ群までの距離は１２１ｍｍに設定されている。
【００９８】
この第４の実施例の収差状況は、夫々図１７（焦点距離４５ｍｍ時）、図１８（焦点距離１４４ｍｍ時）、図１９（焦点距離３６０ｍｍ時）に示す通りである。
【００９９】
本発明の第５の実施例は、図５に示す通りの構成である。対物レンズの後方から順に、正の屈折力の第１レンズ群Ｇ１と、負の屈折力の第２レンズ群Ｇ２と、正の屈折力の第３レンズ群Ｇ３と、負の屈折力の第４レンズ群Ｇ４にて構成されている。そして、低倍端から高倍端への変倍に際して、第２レンズ群Ｇ２、第３レンズ群Ｇ３、第４レンズ群Ｇ４が光軸に沿って移動する。この時、第１レンズ群Ｇ１から第２レンズ群Ｇ２の間隔が短くなり、第２レンズ群Ｇ２から第３レンズ群Ｇ３の間隔が長くなり、第３レンズ群Ｇ３から第４レンズ群Ｇ４の間隔が長くなる。
【０１００】
また、この第５の実施例は、第１レンズ群Ｇ１が凸レンズと、凸レンズと凹レンズとを接合したパワーの弱い接合負レンズからなる前群Ｇ１Ｆと、正レンズよりなる後群Ｇ１Ｒとにて構成されている。また、第２レンズ群Ｇ２が、負のメニスカスレンズと正のメニスカスレンズとを接合した接合負メニスカスレンズにて構成されている。また、第３レンズ群Ｇ３が、負のメニスカスレンズと凸レンズとを接合した接合正レンズと、正レンズとにて構成されている。更に第４レンズ群Ｇ４は、像面側に凹面を向けた負メニスカスレンズと、第２レンズ群側に強い凹面を向けた両凹レンズと両凸レンズとを接合した接合負レンズと、凸レンズとにて構成されている。
【０１０１】
この第５の実施例の光学系中に、二つの開口絞りＳ１（１２面）、Ｓ２（１８面）を配置する。低倍端では対物レンズの瞳共役位置が第３レンズ群Ｇ３の近傍にあるので、開口絞りＳ１を第３レンズ群近傍に配置する。また中間倍率では、対物レンズの瞳共役位置が、第３レンズ群Ｇと第４レンズ群の間にあるので、開口絞りＳ２を第３レンズ群Ｇ３と第４レンズ群Ｇ４の間に配置する。つまり低倍端では、対物レンズの開口を制限するように開口絞りＳ１の径を絞り、開口絞りＳ２の径を開放にする。また中間倍率では、開口絞りＳ１の径を開放にし、対物レンズの開口を制限するように開口絞りＳ２の径を制限する。高倍端では、開口絞りＳ１、Ｓ２の径を開放する。
【０１０２】
前述のように、第５の実施例では、図５の（Ａ）低倍端、（Ｂ）中間倍率、（Ｃ）高倍端に示すように、第２レンズ群Ｇ２、第３レンズ群Ｇ３、第４レンズ群Ｇ４を移動させている。この変倍によって、焦点距離が４５ｍｍ（低倍端）から１４４ｍｍ（中間倍率）、更に３６０ｍｍ（高倍端）まで変化する。なお、焦点距離４５ｍｍの時の視野数が８であり、それ以外の焦点距離では視野数が１１である。
【０１０３】
また、焦点距離が４５ｍｍから１４４ｍｍまでは、射出側開口数が０．０３２となるように開口絞りＳ１、Ｓ２の径を設定してある。また、焦点距離が１４４ｍｍから３６０ｍｍまでは、開口絞りＳ１、Ｓ２を開放としている。これにより、対物レンズの瞳径１４．４ｍｍを、開口絞りＳ１、Ｓ２によって制限しない構成にしている。この結果、低倍端では像面の明るさが一定に保たれ、周辺での光量の減少を抑えることができる。
【０１０４】
この第５の実施例は、条件（１）乃至条件（７）を満足している。これにより、高い変倍比で収差性能の優れた光学系を実現し得るようにしている。
【０１０５】
また、第５の実施例は、４つのレンズ群にて構成することにより、像面での主光線の入射角度が、変倍のどの状態においても約２度に抑えてある。すなわち、ＣＣＤ素子に特有の現象である色シェーディングを抑える上で有効な構成になっている。
【０１０６】
更に、この第５の実施例は、第１レンズ群が条件（８）を満足するように構成されている。これにより、変倍時の第２レンズ群の移動量が少なくでき、レイアウト上も好ましい。また、対物レンズの構成については述べていないが、対物レンズの瞳径は１４．４ｍｍで、対物レンズの瞳位置から第１レンズ群までの距離は１２１ｍｍに設定されている。
【０１０７】
この第５の実施例の収差状況は、夫々図２０（焦点距離４５ｍｍ時）、図２１（焦点距離１４４ｍｍ時）、図２２（焦点距離３６０ｍｍ時）に示す通りである。
【０１０８】
本発明のズーム撮影光学系の第６の実施例は、図６に示す通りの構成である。対物レンズの後方から順に、正の屈折力を持つ第１レンズ群Ｇ１と、負の屈折力を持つ第２レンズ群Ｇ２と、正の屈折力を持つ第３レンズ群Ｇ３と、正の屈折力を持つ第４レンズ群Ｇ４とで構成されている。そして、低倍端から高倍端への変倍の際に、第２レンズ群Ｇ２、第３レンズ群Ｇ３、第４レンズ群Ｇ４が光軸に沿って移動する。この時、第１レンズ群Ｇ１と第２レンズ群Ｇ２の間隔が短くなり、第２レンズ群Ｇ２と第３レンズ群Ｇ３の間隔がいったん短くなってから長くなり、第３レンズ群Ｇ３と第４レンズ群Ｇ４の間隔が長くなる。
【０１０９】
また、第６の実施例は、第１レンズ群Ｇ１が凸レンズと、凸レンズと凹レンズとを接合したパワーの弱い接合負レンズよりなる前群Ｇ１Ｆと、正レンズよりなる後群Ｇ１Ｒとにて構成される。また第２レンズ群Ｇ２は、負メニスカスレンズと正メニスカスレンズとを接合した接合負メニスカスレンズにて構成される。また第３レンズ群Ｇ３は、負メニスカスレンズと凸レンズとを接合した接合正レンズと、正レンズとより構成されている。更に第４レンズ群Ｇ４は、像面側に凹面を向けた負メニスカスレンズと、両凹レンズと両凸レンズとを接合した接合負レンズと凸レンズとにて構成されている。
【０１１０】
この第６の実施例の光学系中に、二つの開口絞りＳ１（１２面）、Ｓ２（１８面）を配置する。低倍端では対物レンズの瞳共役位置が第３レンズ群Ｇ３の近傍にあるので、開口絞りＳ１を第３レンズ群近傍に配置する。また中間倍率では、対物レンズの瞳共役位置が、第３レンズ群Ｇと第４レンズ群の間にあるので、開口絞りＳ２を第３レンズ群Ｇ３と第４レンズ群Ｇ４間に配置する。つまり低倍側では、対物レンズの開口を制限するように開口絞りＳ１の径を絞り、開口絞りＳ２の径を開放にする。また中間倍率では、開口絞りＳ１の径を開放にし、対物レンズの開口を制限するように開口絞りＳ２の径を制限する。高倍端では、開口絞りＳ１、Ｓ２の径を開放する。
【０１１１】
前述のように、第６の実施例では、図６の（Ａ）低倍端、（Ｂ）中間倍率、（Ｃ）高倍端に示すように、第２レンズ群Ｇ２、第３レンズ群Ｇ３、第４レンズ群Ｇ４を移動させている。この変倍によって、焦点距離が４５ｍｍ（低倍端）から１４４ｍｍ（中間倍率）、更に３６０ｍｍ（高倍端）まで変化する。なお、焦点距離４５ｍｍの時の視野数が８であり、それ以外の焦点距離では視野数が１１である。
【０１１２】
また、焦点距離が４５ｍｍから１４４ｍｍまでは、射出側開口数が０．０３２となるように開口絞りＳ１、Ｓ２の径を設定してある。また、焦点距離が１４４ｍｍから３６０ｍｍまでは、開口絞りＳ１、Ｓ２を開放としている。これにより、対物レンズの瞳径１４．４ｍｍを、開口絞りＳ１、Ｓ２によって制限しない構成になっている。この結果、低倍端では像面の明るさが一定に保たれ、周辺での光量の減少を抑えることができる。
【０１１３】
この第６の実施例は、条件（１）乃至条件（７）を満足し、これにより高い変倍比で収差性能の優れた光学系を実現し得る。
【０１１４】
第６の実施例は、４つのレンズ群にて構成することにより、像面での主光線の入射角度が、変倍のどの状態においても約２度に抑えてある。すなわち、ＣＣＤ素子に特有の現象である色シェーディングを抑える上で有効な構成になっている。
【０１１５】
更に、第６の実施例は、第１レンズ群が条件（８）を満足するように構成されている。これにより、第２レンズ群の移動量を少なくすることができ、レイアウト上も好ましい。また、対物レンズの構成は述べていないが、対物レンズの瞳径は１４．４ｍｍであり、対物レンズの瞳位置からズーム撮影光学系の第１レンズ群までの距離は１２１ｍｍに設定されている。
【０１１６】
この第６の実施例の収差状況は、夫々図２３（焦点距離４５ｍｍ時）、図２４（焦点距離１４４ｍｍ時）、図２５（焦点距離３６０ｍｍ時）に示す通りである。
【０１１７】
本発明の第７の実施例は、図７に示す通りの構成である。つまり、対物レンズの後方から順に、正の屈折力を持つ第１レンズ群Ｇ１と、負の屈折力を持つ第２レンズ群Ｇ２と、正の屈折力を持つ第３レンズ群Ｇ３と、正の屈折力を持つ第４レンズ群Ｇ４と、負の屈折力を持つ第５レンズ群Ｇ５で構成されている。そして、低倍端から高倍端へ変倍する際に、第２レンズ群Ｇ２、第３レンズ群Ｇ３、第４レンズ群Ｇ４が光軸に沿って移動する。この時、第１レンズ群Ｇ１と第２レンズ群Ｇ２との間隔が短くなり、第２レンズ群Ｇ２と第３レンズ群Ｇ３の間隔がいったん短くなってから長くなり、第３レンズ群Ｇ３と第４レンズ群Ｇ４の間隔が長くなってから短くなり、第４レンズ群Ｇ４と第５レンズ群Ｇ５の間隔が長くなる。
【０１１８】
また、第７の実施例は、第１レンズ群Ｇ１が凸レンズと、凸レンズと凹レンズとを接合したパワーの弱い接合正レンズよりなる前群Ｇ１Ｆと、正レンズよりなる後群Ｇ１Ｒとにて構成されている。第２レンズ群Ｇ２は、負メニスカスレンズと正メニスカスレンズの接合メニスカスレンズで構成されている。また、第３レンズ群Ｇ３は、負メニスカスレンズと凸レンズとを接合した接合正レンズで構成されている。また第４レンズ群Ｇ４は、メニスカス正レンズと、負メニスカスレンズと凸レンズを接合した接合正レンズにて構成されている。更に第５レンズ群Ｇ５は、両凹レンズと、両凹レンズと正レンズとを接合した接合メニスカス負レンズと、正メニスカスレンズにて構成されている。
【０１１９】
この第７の実施例は、第３レンズ群Ｇ３と第４レンズ群Ｇ４の間に、対物レンズの瞳位置と共役な位置がある。そして、この瞳共役位置の近傍に、開口絞りＳが配置されている。また、開口絞りＳは、変倍時に第４レンズ群Ｇ４と一体に光軸上を移動するようにしている。
【０１２０】
前述のように、第７の実施例では、図７の（Ａ）低倍端、（Ｂ）中間倍率、（Ｃ）高倍端に示すように、第２レンズ群Ｇ２、第３レンズ群Ｇ３、第４レンズ群Ｇ４を移動させている。この変倍によって、焦点距離が４５ｍｍ（低倍端）から１８０ｍｍ（中間倍率）、更に９００ｍｍ（高倍端）まで変化する。なお、焦点距離４５ｍｍの時の視野数が８であり、それ以外の焦点距離では視野数が１１である。　　また、焦点距離が４５ｍｍから１８０ｍｍまでは、射出側開口数が０．０３２となるように開口絞りＳの径を設定している。そして、焦点距離が１８０ｍｍから９００ｍｍまでは、開口絞りＳの径を開放としている。これにより、対物レンズの瞳径１７．０９ｍｍを開口絞りにより制限しない構成にしている。この結果、低倍端では像面の明るさが一定に保たれ、周辺での光量の減少を抑えることができる。
【０１２１】
この第７の実施例は、第３レンズ群の移動量が少ないため、像面Ｉにおける主光線の入射角が変倍中のどの状態でも約２度以内に抑えられている。すなわち、ＣＣＤ素子に特有の現象である色シェーディングを抑える上で有効な構成になっている。
【０１２２】
この第７の実施例では対物レンズの構成は記載していないが、対物レンズの瞳径は１７．０９ｍｍであり、対物レンズの瞳位置から第１レンズ群Ｇ１までの距離は１７１ｍｍである。
【０１２３】
この第７の実施例の収差状況は、夫々図２６（焦点距離４５ｍｍ時）、図２７（焦点距離１８０ｍｍ時）、図２８（焦点距離９００ｍｍ時）に示す通りである。
【０１２４】
尚、各実施例の収差図中、ＦＩＹは像高である。
【０１２５】
以上述べた本発明の実施例１、２、３、７のズーム光学系は、例えば、倍率２０倍、焦点距離９ｍｍ、開口数０．９の対物レンズと組み合わせて使用することができる。この場合、低倍端では総合倍率が５倍で開口数が０．１６になる。また、高倍端では総合倍率が１００倍で、開口数が０．９になる。このように、総合倍率が５から１００倍、開口数０．１６から０．９での観察、撮影が可能になる。
【０１２６】
しかも、低倍端では開口絞りＳによりけられを抑えることができるので、収差性能を向上させることができる。また、撮像面に入射する主光線角度が２度以下となるように構成されているので、ＣＣＤ素子等の撮像素子においてシェーディングが発生せず良好な撮影が可能である。
【０１２７】
本発明のズーム撮影光学系は、以上詳細に述べた通りであり、特許請求の範囲の各項に記載する構成のほか、次の各項に記載するものも本発明の目的を達成し得る。
【０１２８】
［１］特許請求の範囲の請求項３に記載する光学系で、前記第１レンズ群が正レンズと負レンズとよりなる接合レンズを少なくとも含む複数のレンズ成分よりなり、前記最終像に最も近いレンズ群中に前記中間像側に凹面を向けた負の屈折力のレンズを少なくとも一つ備え、下記条件（６）、（７）を満足するズーム撮影光学系。
（６）　　νＰ−νＮ≧３０
（７）　　Ｇｎ≧１．６
ただし、
νＰは第１レンズ群中の接合レンズの正レンズのアッベ数、
νＮは第１レンズ群中の接合レンズの負レンズのアッベ数、
Ｇｎは前記中間像側に凹面を向けた負の屈折力のレンズの屈折率である。
【０１２９】
［２］　前記［１］に記載する光学系で、前記第１レンズ群が前群と後群とよりなり、下記条件（８）を満足するズーム撮影光学系。
（８）　　０．３＜Ｄ１１／Ｄ１＜０．８
ただし、Ｄ１１は前記前群と後群の間隔である。
【０１３０】
［３］　特許請求の範囲の請求項１に記載する光学系で、前記正の屈折力の第３レンズ群の像側に負の屈折力の第４レンズ群を配置したズーム撮影光学系。
【０１３１】
［４］　特許請求の範囲の請求項１に記載する光学系で、前記正の屈折力の第３レンズ群の像側に正の屈折力の第４レンズ群を配置したズーム撮影光学系。
【０１３２】
［５］　特許請求の範囲の請求項１に記載する光学系で、前記正の屈折力の第３レンズ群の像側に、対物レンズ側より、正の屈折力の第４レンズ群と正の屈折力の第５レンズ群を配置したズーム撮影光学系。
【０１３３】
［６］　特許請求の範囲の請求項１に記載する光学系で、前記正の屈折力の第３レンズ群の像側に、対物レンズ側より、正の屈折力の第４レンズ群と負の屈折力の第５レンズ群を配置したズーム撮影光学系
【０１３４】
【発明の効果】
本発明のズーム撮影光学系は、顕微鏡の対物レンズによる物体像を撮像素子に結像させるもので、高い光学性能を保ちながら２０倍の高変倍比を持ち、操作性やシステム性を向上させ得る等の効果を有する。
【図面の簡単な説明】
【図１】本発明の第１の実施例の構成を示す図
【図２】本発明の第２の実施例の構成を示す図
【図３】本発明の第３の実施例の構成を示す図
【図４】本発明の第４の実施例の構成を示す図
【図５】本発明の第５の実施例の構成を示す図
【図６】本発明の第６の実施例の構成を示す図
【図７】本発明の第７の実施例の構成を示す図
【図８】第１の実施例の焦点距離４５ｍｍでの収差曲線図
【図９】第１の実施例の焦点距離１８０ｍｍでの収差曲線図
【図１０】第１の実施例の焦点距離９００ｍｍでの収差曲線図
【図１１】第２の実施例の焦点距離４５ｍｍでの収差曲線図
【図１２】第２の実施例の焦点距離１８０ｍｍでの収差曲線図
【図１３】第２の実施例の焦点距離９００ｍｍでの収差曲線図
【図１４】第３の実施例の焦点距離４５ｍｍでの収差曲線図
【図１５】第３の実施例の焦点距離１８０ｍｍでの収差曲線図
【図１６】第３の実施例の焦点距離９００ｍｍでの収差曲線図
【図１７】第４の実施例の焦点距離４５ｍｍでの収差曲線図
【図１８】第４の実施例の焦点距離１４４ｍｍでの収差曲線図
【図１９】第４の実施例の焦点距離３６０ｍｍでの収差曲線図
【図２０】第５の実施例の焦点距離４５ｍｍでの収差曲線図
【図２１】第５の実施例の焦点距離１４４ｍｍでの収差曲線図
【図２２】第５の実施例の焦点距離３６０ｍｍでの収差曲線図
【図２３】第６の実施例の焦点距離４５ｍｍでの収差曲線図
【図２４】第６の実施例の焦点距離１４４ｍｍでの収差曲線図
【図２５】第６の実施例の焦点距離３６０ｍｍでの収差曲線図
【図２６】第７の実施例の焦点距離４５ｍｍでの収差曲線図
【図２７】第７の実施例の焦点距離１８０ｍｍでの収差曲線図
【図２８】第７の実施例の焦点距離９００ｍｍでの収差曲線図[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical system used in an optical device having a microscope objective lens, and more particularly to a zoom photographing optical system capable of changing the size of a sample image formed on an image sensor.
[0002]
[Prior art]
In a conventional optical device such as a microscope, observation and photographing are performed in the following procedure, for example. First, a position to be observed in a wide field of view is searched for using a low-magnification objective lens. Next, the object (sample) is enlarged by conversion (exchange) to a high-magnification objective lens. Then, the enlarged object is observed as it is, or an image is taken by an imaging device. At this time, the magnification range extends from about 1 to 100 times. Therefore, various methods have been proposed as methods for observing or photographing an object over such a wide magnification range.
[0003]
Conventional examples of projecting a sample image by a microscope onto a silver halide film or the like are described in JP-A-5-119265, JP-A-6-281865, and JP-A-10-62692. Are known. The micrograph lenses described in these publications have a magnification of 2 to 5 times.
[0004]
Further, as a low-magnification photographic lens or a variable power lens for photographing a television, a variable power lens capable of photographing at a magnification of about 0.25 to about 4 times in combination with an imaging lens is known.
[0005]
Japanese Patent Application Laid-Open Nos. 4-304409, 9-274137, and 7-56087 disclose conventional examples in which an imaging lens disposed behind a microscope objective lens is a zoom lens. What is described is known. Further, as a conventional example in which a light beam emitted from an objective lens is divided and photographing optical systems of different magnifications are arranged, there are known conventional examples described in JP-A-8-19056 and JP-A-11-183124. I have.
[0006]
There is also known a method of observing and photographing an object image using an afocal zoom lens for a stereomicroscope.
[0007]
[Problems to be solved by the invention]
Among the conventional examples, the photographic optical systems described in JP-A-5-119265, JP-A-6-281865 and JP-A-10-62692 have a fixed photographic magnification of the optical system. . Therefore, when photographing by changing the magnification, it is necessary to convert the photographing optical system arranged in the photographing optical path to a photographing optical system having a different magnification, and the operability is poor.
[0008]
Further, the optical systems described in JP-A-4-304409 and JP-A-9-274137 among the conventional examples are such that an imaging lens disposed behind an objective lens is a zoom lens. This has the advantage that the shooting magnification can be changed continuously. However, since it is a variable magnification system in which the magnification is increased, it cannot be used for observation and photographing at a low magnification. Also, the zoom ratio is as low as about 2 to 3 times.
[0009]
The optical system described in JP-A-7-84189 is a zoom lens having a zoom ratio of about 10 times. However, the position of the exit pupil fluctuates, which is not very desirable. Further, since there is no pupil position of the objective lens in the lens system, the numerical aperture on the exit side at low magnification becomes large. As a result, blurring around the image plane becomes large. Further, the numerical aperture at high magnification is only about 0.6, and the resolution is not sufficient. In addition, since the back focus is long, the device becomes large.
[0010]
Further, in the conventional examples described in JP-A-8-19056 and JP-A-11-183124, an optical path is divided so that one is a low magnification side optical path and the other is a high magnification side optical path. . Thereby, there is an advantage that switching between low magnification and high magnification can be easily performed. However, in such a configuration, operability is poor because observation is performed at a fixed magnification.
[0011]
The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a zoom photographing optical system having a wide zoom range from a magnification lower than the magnification of an objective lens to more than 10 times. Another object of the present invention is to provide a zoom optical system capable of limiting the size of a light beam at a low magnification. Another object of the present invention is to provide a zoom photographing optical system in which the fluctuation of the exit pupil is suppressed.
[0012]
[Means for Solving the Problems]
The zoom photographing optical system of the present invention is an optical system that is used in an optical device having an objective lens and forms a final image of a sample. The first lens group having a positive refractive power and a negative lens are sequentially arranged from the objective lens. It has at least a second lens group having a refractive power and a third lens group having a positive refractive power, and at the time of zooming from the low magnification end to the high magnification end, the distance between the first lens group and the second lens group is at the low magnification end. The second lens group and the third lens group are respectively located on the optical axis so that the distance between the second lens group and the third lens group is longer at the high magnification end than at the low magnification end. Along the first lens group and the second lens group at the low magnification end, satisfying the following conditions (1) and (2).
(1) 1 ≦ FH / FL ≦ 3
(2) 3 ≦ MGH / MGL ≦ 20
However,
FH is the focal length of the entire lens group between the first lens group and the intermediate image position at the high magnification end,
FL is the focal length of the entire lens group between the first lens group and the intermediate image position at the low magnification end;
MGH is the magnification of the entire lens group between the intermediate image position at the high magnification end and the final image position,
MGL is the magnification of the entire lens group between the intermediate image position and the final image position at the low magnification end.
[0013]
The zoom photographing optical system of the present invention further satisfies the following conditions (3), (4), and (5).
(3) 0.3 <D1 / D0 <0.7
(4) 0.15 <D2 / D0 <0.7
(5) 0 <FB / D0 <0.3
However,
D0 is the distance from the lens surface closest to the objective lens in the first lens group to the final image position;
D1 is the distance at the low magnification end from the lens surface closest to the objective lens in the first lens group to the intermediate image position;
D2 is the amount of movement of the second lens group when zooming from the low magnification end to the high magnification end,
FB is the distance from the lens surface on the final image side of the lens closest to the final image to the final image.
[0014]
Further, in the zoom photographing optical system of the present invention, a conjugate image of a pupil of an objective lens is formed between the intermediate image and the final image, an aperture stop is arranged at a position of the conjugate image, and a diameter of the aperture stop is adjusted. Is configured to be changed.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
In the zoom optical system according to the present invention, the effect of each lens group on light rays will be described. Some zoom photographing optical systems of the present invention are used in combination with an optical device such as a microscope. Here, it is assumed that the optical device includes an infinity-correction type objective lens. The zoom photographing optical system according to the present invention is disposed behind the objective lens. The light beam emitted from the infinity-correction type objective lens is an infinite light beam (parallel light beam). Therefore, when combined with such an objective lens, the photographic magnification is determined by the focal length of the zoom photographic optical system of the present invention and the focal length of the objective lens.
[0016]
In the zoom optical system according to the present invention, the first lens group having a positive power has an effect of converging an incident light beam at infinity. Further, the second lens group having negative power has an effect of diverging the light flux from the first lens group. Further, the third lens group or the lens groups subsequent to the third lens group have a positive power as a whole, and converge a light beam from the second lens group to a predetermined position by a converging action. The zoom photographing optical system according to the present invention is configured to form an intermediate image between the first lens group and the second lens group at the low magnification end. Further, an image conjugate with the pupil of the objective lens (hereinafter, referred to as a pupil conjugate image) is formed at a predetermined position between the intermediate image and the final image. At the high magnification end, the pupil conjugate image is formed at a predetermined position from the intermediate image position to a lens group closest to the final image (hereinafter, referred to as a final lens group). It is configured as follows.
[0017]
The zoom optical system of the present invention satisfies the following conditions (1) and (2).
(1) 1 ≦ FH / FL ≦ 3
(2) 3 ≦ MGH / MGL ≦ 20
However,
FH is the focal length of the entire lens group between the first lens group and the intermediate image position at the high magnification end,
FL is the focal length of the entire lens group between the first lens group and the intermediate image position at the low magnification end;
MGH is the magnification of the entire lens group between the intermediate image position at the high magnification end and the final image position,
MGL is the magnification of the entire lens group between the intermediate image position and the final image position at the low magnification end.
[0018]
When the value goes below the lower limit of the condition (1), FL> FH. In this case, the second lens unit having a negative refractive power moves toward the first lens unit from the position of the intermediate image at the low magnification end. Therefore, a zoom photographing optical system cannot be configured. On the other hand, when the value goes below the lower limit of the condition (2), a necessary zoom ratio cannot be obtained. When the above condition is satisfied, it is possible to perform imaging without deteriorating the brightness of the image while utilizing the resolution of the objective lens in a practically effective magnification range.
[0019]
When the zoom photographing optical system of the present invention includes three lens groups, from the objective lens side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens having a positive refractive power. Arrange in order of group. In this configuration, the second lens group that is a moving group mainly has a zooming action, and the third lens group that is another moving group moves the principal point position of the optical system from the intermediate image position to the final image position. Work to make it work.
[0020]
That is, at the low magnification end, the positions of the second and third lens groups are set such that the magnification of the entire lens group between the intermediate image position and the final image position becomes the reduction magnification. Therefore, when the magnification is changed from the high magnification end to the low magnification end, the principal point position of the optical system between the intermediate image position and the final image position is shifted to the final image side. At the high magnification end, the positions of the second and third lens groups are set such that the magnification of the entire lens group between the intermediate image position and the final image position becomes the magnification. Therefore, when the magnification is changed from the low magnification end to the high magnification end, the principal point position of the optical system between the intermediate image position and the final image position is shifted to the intermediate image side.
[0021]
Therefore, when zooming toward the low magnification end, the distance between the first lens group and the second lens group is increased, and the distance between the second lens group and the third lens group is shortened. The third lens group is moved along the optical axis. Further, as described above, an intermediate image that is a conjugate image of the object is formed between the first lens group and the second lens group.
[0022]
In the case of zooming toward the high magnification end, the distance between the first lens group and the second lens group is reduced, and the distance between the second lens group and the third lens group is increased. The three lens groups are moved along the optical axis. When the second lens group moves toward the objective lens side from the rear focal position of the first lens group, the intermediate image position at the high magnification end is different from the position at the low magnification end.
[0023]
Here, if the focal length of the entire zoom photographing optical system is FT, the focal length at the low magnification end is FT (L), and the focal length at the high magnification end is FT (H), FT (L), FT (H) Are as follows respectively.
FT (L) = FL × MGL
FT (H) = FH × MGH
[0024]
Therefore, the zoom ratio Z is as follows.

That is, the zoom ratio Z of the zoom photographing optical system can be expressed by the product of the condition (1) and the condition (2).
[0025]
As described above, the zoom photographing optical system according to the present invention includes, in order from the objective lens side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. It has at least a lens group. In such a zoom photographing optical system of the present invention, when a lens group is further disposed on the image side than the third lens group, an optical system having the following configuration is desirable.
[0026]
When one lens group is arranged after the third lens group, it is desirable to arrange a fourth lens group having a positive refractive power. Then, at the time of zooming from the low-magnification end to the high-magnification end, it is desirable that the distance between the third lens group and the fourth lens group is initially long and short in the middle.
[0027]
That is, when the zoom photographing optical system of the present invention includes four lens groups, the first lens group having a positive refractive power, the second lens group having a negative refractive power, and the positive refractive power are arranged from the objective lens side. The third lens group and the fourth lens group having a positive refractive power are arranged in this order. Then, at the time of zooming from the low-magnification end to the high-magnification end, the distance between the first lens group and the second lens group is shortened, and the distance between the third lens group and the fourth lens group is initially long and short. The second, third, and fourth lens groups are configured to move along the optical axis, respectively. Then, an intermediate image is formed between the first lens group and the second lens group at the low magnification end, and the above conditions (1) and (2) are satisfied.
[0028]
When one lens group is arranged following the third lens group, a fourth lens group having a negative refractive power may be arranged as another configuration. Then, at the time of zooming from the low magnification end to the high magnification end, it is desirable that the distance between the third lens unit and the fourth lens unit be long.
[0029]
That is, when the zoom optical system of the present invention includes four lens groups, the first lens group having a positive refractive power, the second lens group having a negative refractive power, and the second lens group having a positive refractive power are arranged from the objective lens side. The third lens group and the fourth lens group having negative refractive power are arranged in this order. At the time of zooming from the low-magnification end to the high-magnification end, the distance between the first lens group and the second lens group becomes longer first and then becomes shorter, and then the distance between the second lens group and the third lens group becomes shorter first. The second, third, and fourth lens groups are configured to move along the optical axis, respectively, such that the distance between the third lens group and the fourth lens group becomes longer. Then, an intermediate image is formed between the first lens group and the second lens group at the low magnification end, and the above conditions (1) and (2) are satisfied.
[0030]
In the zoom photographing optical system according to the present invention, when two lens groups are arranged subsequent to the third lens group, a fourth lens group having a positive refractive power and a positive refractive power or a negative refractive power are sequentially arranged from the third lens group. A configuration in which a fifth lens group having a refractive power of? When the magnification is changed from the low-magnification end to the high-magnification end, the distance between the third lens unit and the fourth lens unit becomes longer after the distance between the third lens unit and the fourth lens unit becomes longer. Is desirably moved so that the interval between the two becomes longer.
[0031]
That is, when the zoom photographing optical system of the present invention includes five lens groups, the first lens group having a positive refractive power, the second lens group having a negative refractive power, and the second lens group having a positive refractive power are arranged from the objective lens side. Three lens groups, a fourth lens group having a positive refractive power, and a fifth lens group having a positive refractive power are arranged in this order. Then, at the time of zooming from the low magnification end to the high magnification end, the distance between the first lens group and the second lens group becomes shorter, the distance between the second lens group and the third lens group becomes longer, and the third lens group and the third lens group become longer. The second, third, and fourth lens groups are respectively moved along the optical axis such that the distance between the four lens groups becomes longer at first and then becomes shorter, and the distance between the fourth lens group and the fifth lens group becomes longer. The configuration is as follows. Then, an intermediate image is formed between the first lens group and the second lens group, and the conditions (1) and (2) are satisfied.
[0032]
In another example in which the zoom optical system of the present invention includes five lens groups, the first lens group having a positive refractive power, the second lens group having a negative refractive power, and the positive refractive power are arranged from the objective lens side. , A fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power. Then, at the time of zooming from the low magnification end to the high magnification end, the distance between the first lens group and the second lens group becomes shorter, the distance between the second lens group and the third lens group becomes longer, and the third lens group and the third lens group become longer. The second, third, and fourth lens groups are respectively moved along the optical axis such that the distance between the four lens groups is initially long and then short, and the distance between the fourth lens group and the fifth lens group is long. The configuration is as follows. Then, an intermediate image is formed between the first lens group and the second lens group at the low magnification end, and the above conditions (1) and (2) are satisfied.
[0033]
It is desirable that the zoom photographing optical system of the present invention in each of the above configurations satisfies the following conditions (3), (4), and (5).
(3) 0.3 <D1 / D0 <0.7
(4) 0.15 <D2 / D0 <0.7
(5) 0 <FB / D0 <0.3
However,
D0 is the distance from the lens surface closest to the objective lens in the first lens group to the final image position;
D1 is the distance at the low magnification end from the lens surface closest to the objective lens in the first lens group to the intermediate image position;
D2 is the amount of movement of the second lens group when zooming from the low magnification end to the high magnification end,
FB is the distance from the lens surface on the final image side of the lens closest to the final image to the final image.
[0034]
In the zoom photographing optical system of the present invention, if the condition (3) is satisfied, off-axis aberrations at the low magnification end and spherical aberrations at the high magnification end can be favorably corrected. By satisfying the condition (4), a high zoom ratio can be achieved. By satisfying the condition (5), the back focus of the zoom photographing optical system can be made appropriate and a compact configuration can be realized.
[0035]
In the condition (3), when the value of D1 / D0 is smaller than the lower limit of 0.3, the distance from the first lens group to the intermediate image position becomes short, and the refractive power of the first lens group becomes strong. At this time, when the off-axis principal ray at the low magnification end is incident on the second lens group, the ray height is increased and the incident angle is increased. Therefore, off-axis aberrations and pupil aberrations at the low magnification end also deteriorate, which is not preferable. On the other hand, when the value exceeds the upper limit of 0.7, the power of the first lens unit becomes weak, and the interval from the intermediate image position to the final image position becomes too short. Therefore, in the case of a photographing optical system including three lens groups, the moving space of the second lens group and the third lens group becomes small. In the case of a photographing optical system including four or five lens groups, the moving space of the second lens group, the third lens group, and the fourth lens group is reduced. As a result, a high zoom ratio cannot be obtained in any case.
[0036]
In the condition (4), when the value of D2 / D0 is smaller than the lower limit of 0.15, the negative power of the second lens group becomes too strong. As a result, astigmatism and coma deteriorate at the low magnification end, and spherical aberration worsens at the high magnification end. When the value exceeds the upper limit value 0.7 of the condition (4), the negative power of the second lens unit becomes weak. As a result, a high zoom ratio cannot be obtained. In addition, the amount of movement of the third lens group or the third and fourth lens groups becomes small, and it becomes difficult to keep the image plane position constant.
[0037]
In the condition (5), when FB / D0 becomes smaller than the lower limit value 0, the final image is formed at a position close to the final lens group. Therefore, when the photographing device is to be arranged, structural interference occurs with the final lens group. In the condition (5), when FB / D0 is larger than the upper limit of 0.3, the interval from the first lens unit to the last lens unit becomes short. As a result, it becomes difficult to obtain a high zoom ratio.
[0038]
In the zoom photographing optical system of the present invention in each of the above configurations, it is preferable that an image conjugate with the pupil of the objective lens (pupil conjugate image) is formed between the intermediate image and the final image. At this time, it is preferable that an aperture stop is arranged at or near the position of the pupil conjugate image, and the aperture stop moves on the optical axis according to the magnification. When the position of the aperture stop is fixed, it is preferable to change the diameter of the aperture stop. In this way, the diameter of the light beam passing through the objective lens can be changed.
[0039]
As described above, if the aperture stop is arranged at or near the pupil conjugate position and the diameter of the aperture stop can be changed, the numerical aperture at the low magnification end is limited to reduce the amount of light in the periphery. Can be suppressed. In addition, off-axis aberration performance can be improved. Also, when observing or photographing at low magnification, it may be preferable to give priority to securing the amount of light in the periphery and to reduce blurring rather than the resolving power in some cases. The above configuration is also effective from such a point. Also, by changing the diameter of the aperture stop according to the magnification, the exit-side numerical aperture on the final image plane side can be made constant. This makes it possible to keep the brightness of the image constant during zooming.
[0040]
On the other hand, at the high magnification end, it is desired not to limit the numerical aperture because a resolving power is required. However, there are also cases where the depth of focus is increased by narrowing the aperture stop for observation. Therefore, it is preferable that the diameter of the aperture stop can be changed.
[0041]
In order to fix the position of the aperture stop in the optical path regardless of zooming, it is preferable to dispose the aperture stop between the third lens group and the last lens group. In that case, the exit pupil position becomes constant at all magnifications.
[0042]
Alternatively, a plurality of aperture stops may be provided between the intermediate image position and the final image position. The diameter of the aperture stop arranged near the pupil conjugate position in each magnification is appropriately reduced, and the other aperture stops are opened. Accordingly, even when the pupil conjugate position moves on the optical axis, the aperture of the objective lens can be restricted by setting the plurality of aperture stops to an appropriate diameter, which is a preferable configuration.
[0043]
In the above-described zoom photographing optical system of the present invention, it is preferable that the first lens group is constituted by a plurality of lens components and further includes at least a cemented lens composed of a positive lens and a negative lens. It is also desirable that the final lens group is composed of a plurality of lens groups, and includes a lens having a negative refractive power with a concave surface facing the intermediate image side.
[0044]
In the above configuration, it is preferable that the following conditions (6) and (7) are satisfied.
(6) νP−νN ≧ 30
(7) Gn ≧ 1.6
However,
νP is the Abbe number of the positive lens of the cemented lens in the first lens group,
νN is the Abbe number of the negative lens of the cemented lens in the first lens group,
Gn is the refractive index of the lens having a negative refractive power with the concave surface facing the intermediate image side.
[0045]
When the condition (6) is satisfied, the spherical aberration at the high magnification end and the chromatic aberration of magnification at the low magnification end can be favorably corrected. In the condition (6), when the value of νP−νN is smaller than the lower limit of 30, it becomes difficult to correct spherical aberration at the high magnification end and chromatic aberration of magnification at the low magnification end.
[0046]
If the condition (7) is satisfied, the Petzval sum can be reduced to correct the field curvature. Also, coma and astigmatism in the entire zoom range can be corrected well. In the condition (7), when the lower limit value of Gn is smaller than 1.6, the radius of curvature of a lens having a negative refractive power whose concave surface faces the intermediate image side becomes small. Therefore, it becomes difficult to satisfactorily correct coma and astigmatism over the entire zoom range.
[0047]
It is preferable that the zoom photographing optical system be configured with a cemented lens instead of a single lens in order to correct aberration in each lens group. This makes it possible to favorably correct aberrations over the entire zoom range.
[0048]
In the zoom photographing optical system of the present invention, the first lens group includes two lens components having a positive refractive power (a front group and a rear group), and an interval between both lens components (an interval between the front group and the rear group) D11. Preferably satisfies the following condition (8).
(8) 0.3 <D11 / D1 <0.8
Here, D11 is an interval between the front group and the rear group.
[0049]
If the above condition (8) is satisfied, it becomes easy to correct chromatic aberration of magnification at the low magnification end and spherical aberration at the high magnification end. Further, since the principal point position of the first lens group moves to the intermediate image side, the negative refracting power of the second lens group increases. As a result, the amount of movement of the second lens group is reduced, so that the layout is preferable. Further, it is easy to correct chromatic aberration of magnification at the low magnification end and spherical aberration at the high magnification end.
[0050]
In the condition (8), when the value of D11 / D1 is smaller than the lower limit value of 0.3, the amount of movement of the principal point position of the first lens group is reduced, so that the negative refractive power of the second lens group is increased. Can not. Therefore, the amount of movement of the second lens group must be increased during zooming, and the size of the optical system increases. If the upper limit is larger than 0.8, the distance from the rear group of the first lens group to the intermediate image is too short. Therefore, in the rear group of the first lens group, the off-axis principal ray height at the low magnification end and the on-axis ray height at the high magnification end are small. As a result, the effect for aberration correction cannot be obtained. In addition, the amount of movement of the second lens unit during zooming is small, and the zoom ratio of the optical system cannot be increased.
[0051]
Embodiments of the zoom imaging optical system according to the present invention will be described below. The first to seventh embodiments of the present invention have configurations as shown in FIGS. 1 to 7, respectively, and have data shown in the following Tables 1 to 7.
[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

In the above data, the surface numbers 1, 2,... Represent the respective surfaces of the zoom photographing optical system in order from the objective lens side, and the radii of curvature and the intervals corresponding to the respective surface numbers are r1, d1 in FIGS. The refractive indices Nd and Vd indicate the refractive index and Abbe number of the medium between the corresponding surface and the next surface with respect to the d-line. Further, a1, a2, a3, and a4 in the data are variable intervals at the time of zooming, respectively. In the first, second, third, and seventh embodiments, the values of the variable intervals are set when the focal lengths are 45 mm, 180 mm, and 900 mm. In the fourth, fifth, and sixth embodiments, the values of the variable intervals are used when the focal length is 45 mm, 144 mm, and 360 mm. The unit of length such as the radius of curvature, interval, focal length, aperture stop diameter, exit pupil position, and image height is mm. The exit pupil position is a distance (mm) from the final surface.
[0059]
In the first embodiment, as shown in FIG. 1, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group having a positive refractive power are arranged in order from the rear of the objective lens. It comprises a lens group G3, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a positive refractive power. Then, when zooming from the low magnification end to the high magnification end, the second lens group G2, the third lens group G3, and the fourth lens group G4 move along the optical axis. At this time, the distance between the first lens group G1 and the second lens group G2 becomes shorter, the distance between the second lens group G2 and the third lens group G3 becomes longer, and the distance between the third lens group G3 and the fourth lens group G4 increases. Becomes longer and then shorter, and the distance between the fourth lens group G4 and the fifth lens group G5 becomes longer.
[0060]
In the first embodiment, the first lens group G1 includes a front group G1F of a cemented positive lens in which a convex lens and a concave lens are cemented, and a rear group G1R of a convex lens. The second lens group G2 includes a negative cemented meniscus lens in which a negative meniscus lens and a positive meniscus lens are cemented. The third lens group G3 includes a positive cemented lens in which a negative meniscus lens and a positive meniscus lens are cemented. The fourth lens group G4 includes a positive cemented meniscus lens in which a negative meniscus lens and a positive meniscus lens are cemented, and a convex lens. The fifth lens group G5 includes a negative cemented lens in which a biconcave lens and a positive meniscus lens are cemented, a negative cemented meniscus lens in which a biconcave lens and a biconvex lens are cemented, and a convex lens.
[0061]
In the first embodiment, there is a position conjugate with the pupil position of the objective lens between the third lens group G3 and the fourth lens group G4. An aperture stop S is arranged near the pupil conjugate position. The aperture stop S moves on the optical axis integrally with the fourth lens group G4 during zooming.
[0062]
As described above, in the first embodiment, as shown at (A) low magnification end, (B) intermediate magnification, and (C) high magnification end in FIG. 1, the second lens group G2, the third lens group G3, The fourth lens group G4 is moved. As a result, the focal length changes from 45 mm (low magnification end) to 180 mm (intermediate magnification), and further to 900 mm (high magnification end). Note that the number of fields of view at a focal length of 45 mm is 8, and at other focal lengths, the number of fields of view is 11.
[0063]
Also, the diameter of the aperture stop S is set so that the emission side numerical aperture is 0.032 when the focal length is from 45 mm to 180 mm. The aperture stop S is open from a focal length of 180 mm to 900 mm. Thus, the pupil diameter of 17.09 mm of the objective lens is not limited by the aperture stop S. As a result, the brightness of the image plane is kept constant at the low magnification end, and a decrease in the amount of light at the periphery can be suppressed.
[0064]
In the first embodiment, since the amount of movement of the third lens group G3 is small, the incident angle of the principal ray on the image plane I is suppressed to about 2 degrees in any state during zooming. That is, the configuration is effective in suppressing color shading, which is a phenomenon unique to CCD elements.
[0065]
The first embodiment is configured such that an intermediate image IM is formed between the first lens group G1 and the second lens group G2 at the low magnification end. At the intermediate magnification and the high magnification end, the second lens group G2 moves closer to the first lens group G1 than the position IM of the intermediate image at the low magnification end. As a result, the intermediate magnification and the intermediate image position at the high magnification end [IM in FIGS. 1B and 1C] have moved to the image side.
[0066]
At the low magnification end, as shown in FIG. 1A, the intermediate image IM is relayed to the image plane I by the second lens group G2 to the fifth lens group G5. In order to shift the principal point position to the image side, the distance between the intermediate image IM and the second lens group G2 is increased, and the distance between the second lens group G2 and the fifth lens group G5 is reduced. In this way, by arranging the second lens group G2 to the fifth lens group G5 on the image plane side, the magnification is reduced.
[0067]
At the intermediate magnification shown in FIG. 1B, the intermediate image IM is relayed to the image plane I by the third lens group G3 to the fifth lens group G5. The third lens group G3 functions as a field lens for the intermediate image. That is, it serves to eliminate off-axis light flux and correct off-axis aberrations. Further, the fourth lens group G4 moves toward the third lens group G3 from the position at the low magnification end to increase the magnification from the intermediate image IH to the image plane I.
[0068]
Furthermore, at the high magnification end, as shown in FIG. 1C, the intermediate image IM is relayed to the image plane by the optical system from the third lens group G3 to the fifth lens group G5. Further, the third lens group G3 and the fourth lens group G4 are moved to the intermediate image side. As a result, the position of the principal point of the relay optical system is moved to the intermediate image side, and the magnification is realized.
[0069]
The first embodiment satisfies the conditions (1) to (7).
[0070]
Although the configuration of the objective lens is not described in the first embodiment, the pupil diameter of the objective lens is 17.09 m, and the distance from the pupil position of the objective lens to the first lens group G1 is 169 mm.
[0071]
The aberration states of the first embodiment are as shown in FIG. 8 (at a focal length of 45 mm), FIG. 9 (at a focal length of 180 mm), and FIG. 10 (at a focal length of 900 mm), respectively.
[0072]
In the second embodiment of the present invention, as shown in FIG. 2, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and The third lens group G3 has a positive refractive power, the fourth lens group G4 has a positive refractive power, and the fifth lens group G5 has a positive refractive power. Then, at the time of zooming from the low magnification end to the high magnification end, the second lens group G2, the third lens group G3, and the fourth lens group G4 move along the optical axis. At this time, the distance between the first lens group G1 and the second lens group G2 is reduced, the distance between the second lens group G2 and the third lens group G3 is increased, and the distance between the third lens group G3 and the fourth lens group G4 is reduced. Becomes longer and then shorter, and the distance between the fourth lens group G4 and the fifth lens group G5 becomes longer.
[0073]
In the second embodiment, the first lens group G1 is composed of a front group G1F of a negative cemented lens having a weak power in which a concave lens and a convex lens are cemented, and a rear group G1R of a convex lens. The second lens group G2 includes a negative cemented meniscus lens in which a negative meniscus lens and a positive meniscus lens are cemented. The third lens group G3 is composed of a positive cemented lens in which a negative meniscus lens and a convex lens are cemented. The fourth lens group G4 includes a convex lens and a positive cemented lens obtained by cementing a negative meniscus lens and a convex lens. The fifth lens group G5 includes a negative cemented lens in which a biconcave lens and a positive meniscus lens are joined, a positive cemented meniscus lens in which a biconcave lens and a convex lens are joined, and a positive meniscus lens. ing.
[0074]
In the second embodiment, there is a position conjugate with the pupil position of the objective lens between the third lens group G3 and the fourth lens group G4. An aperture stop S is arranged near the pupil conjugate position. The aperture stop S moves on the optical axis integrally with the fourth lens group G4 during zooming.
[0075]
As described above, in the second embodiment, as shown in FIG. 2A (low magnification end), (B) intermediate magnification, and (C) high magnification end, the second lens group G2, the third lens group G3, The fourth lens group G4 is moved. This zooming changes the focal length from 45 mm (low magnification end) to 180 mm (intermediate magnification) and further from 900 mm (high magnification end). Note that the number of fields of view at a focal length of 45 mm is 8, and at other focal lengths, the number of fields of view is 11.
[0076]
Further, the diameter of the aperture stop S is set so that the emission side numerical aperture is 0.032 when the focal length is from 45 mm to 180 mm. The aperture stop S is open when the focal length is between 180 mm and 900 mm. Thus, the pupil diameter of 17.09 mm of the objective lens is not limited by the aperture stop S. As a result, the brightness of the image plane is kept constant at the low magnification end, and a decrease in the amount of light at the periphery can be suppressed.
[0077]
In the second embodiment, since the amount of movement of the third lens group G3 is small, the incident angle of the principal ray on the image plane I is kept within 2 degrees in any state of zooming. That is, the configuration is effective in suppressing color shading, which is a phenomenon unique to CCD elements.
[0078]
The second embodiment also satisfies the conditions (1) to (7). The operation of each lens group is the same as in the first embodiment.
[0079]
Although the configuration of the objective lens is not described in the second embodiment, the pupil diameter of the objective lens is 17.09 m, and the distance from the pupil position of the objective lens to the first lens group G1 is 171 mm.
[0080]
The aberration states of the second embodiment are as shown in FIG. 11 (at a focal length of 45 mm), FIG. 12 (at a focal length of 180 mm), and FIG. 13 (at a focal length of 900 mm).
[0081]
In the third embodiment of the present invention, as shown in FIG. 3, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a positive The third lens group G3 has a refractive power, the fourth lens group G4 has a positive refractive power, and the fifth lens group G5 has a positive refractive power. Then, at the time of zooming from the low magnification end to the high magnification end, the second lens group G2, the third lens group G3, and the fourth lens group G4 move on the optical axis, respectively. At this time, the distance between the first lens group G1 and the second lens group G2 is shortened, the distance between the second lens group G2 and the third lens group G3 is once shortened and then lengthened, and the distance between the third lens group G3 and the fourth lens group G4 is shortened. The distance between the lens groups G4 once increases and then decreases, and the distance between the fourth lens group G4 and the fifth lens group G5 increases.
[0082]
In the third embodiment, the first lens group G1 is divided into a front group G1F including a convex lens, a positive cemented lens having a weak power obtained by cementing the convex lens and the concave lens, and a rear group G1R including a positive lens. It is configured. The second lens group G2 includes a negative cemented lens in which a negative meniscus lens and a positive meniscus lens are cemented. The third lens group G3 is composed of a positive cemented lens in which a negative meniscus lens and a convex lens are cemented. The fourth lens group G4 includes a positive meniscus lens and a positive cemented lens obtained by cementing a negative meniscus lens and a convex lens. The fifth lens group G5 includes a negative meniscus lens having a loose convex surface facing the fourth lens group G4, a negative cemented meniscus lens in which a biconcave lens and a positive lens are cemented, and a positive meniscus lens. I have.
[0083]
In the third embodiment, there is a position conjugate with the pupil position of the objective lens between the third lens group G3 and the fourth lens group G4. An aperture stop S is arranged near the pupil conjugate position. The aperture stop S moves on the optical axis integrally with the fourth lens group G4 during zooming.
[0084]
As described above, in the third embodiment, as shown at (A) low magnification end, (B) intermediate magnification, and (C) high magnification end in FIG. 3, the second lens group G2, the third lens group G3, The fourth lens group G4 is moved. This zooming changes the focal length from 45 mm (low magnification end) to 180 mm (intermediate magnification) and further from 900 mm (high magnification end). Note that the number of fields of view at a focal length of 45 mm is 8, and at other focal lengths, the number of fields of view is 11.
[0085]
Also, the diameter of the aperture stop S is set so that the emission side numerical aperture is 0.032 when the focal length is from 45 mm to 180 mm. The aperture stop S is open when the focal length is from 180 mm to 900 mm. Thus, the pupil diameter of 17.09 mm of the objective lens is not limited by the open stop S. As a result, the brightness of the image plane is kept constant at the low magnification end, and a decrease in the amount of light at the periphery can be suppressed.
[0086]
In the third embodiment, since the amount of movement of the third lens group G3 is small, the incident angle of the principal ray on the image plane I is suppressed to within about 2 degrees in any state of zooming. That is, the configuration is effective in suppressing color shading, which is a phenomenon unique to CCD elements.
[0087]
The third embodiment satisfies the conditions (1) to (8). The operation of each lens group is the same as in the first embodiment.
[0088]
In the third embodiment, the first lens group G1 includes the front group G1F and the rear group G1R, and the amount of movement of the second lens group G2 is small. Although the configuration of the objective lens is not shown, the pupil diameter of the objective lens is 17.09 mm, and the distance from the pupil position of the objective lens to the first lens group G1 is 171 mm.
[0089]
The aberration states of the third embodiment are as shown in FIGS. 14 (at a focal length of 45 mm), FIG. 15 (at a focal length of 180 mm), and FIG. 16 (at a focal length of 900 mm), respectively.
[0090]
The fourth embodiment of the present invention has a configuration as shown in FIG. That is, in order from the rear of the objective lens, the first lens group G1 has a positive refractive power, the second lens group G2 has a negative refractive power, and the third lens group G3 has a positive refractive power. Then, at the time of zooming from the low magnification end to the high magnification end, the second lens group G2 and the third lens group G3 move along the optical axis. At this time, the distance between the first lens group G1 and the second lens group G2 becomes shorter, and the distance between the second lens group G2 and the third lens group G3 becomes longer.
[0091]
In the fourth embodiment, the first lens group G1 includes a front lens group G1F including a convex lens, a cemented lens having a low power obtained by cementing a convex lens and a concave lens, and a rear lens group including a positive lens. Group G1R. The second lens group G2 includes a cemented negative meniscus lens in which a negative meniscus lens and a positive meniscus lens are cemented. Further, the third lens group G3 includes a cemented positive lens in which a negative meniscus lens and a convex lens are cemented, a positive lens, a negative meniscus lens having a strong concave surface facing the image surface side, and a concave surface in the second lens group G2. It is composed of a cemented negative lens in which a biconcave lens and a biconvex lens directed to each other are cemented, and a positive meniscus lens.
[0092]
Two aperture stops S1 (ninth surface) and S2 (25th surface) are arranged in the optical system of the fourth embodiment. Since the pupil conjugate position of the objective lens is near the second lens group G2 at the low magnification end, the aperture stop S1 is arranged near the second lens group. At the intermediate magnification, the pupil conjugate position of the objective lens is near the third lens group G3, so the aperture stop S2 is arranged in the third lens group G3. That is, at the low magnification end, the diameter of the aperture stop S1 is reduced so as to limit the aperture of the objective lens, and the diameter of the aperture stop S2 is opened. At an intermediate magnification, the diameter of the aperture stop S1 is opened, and the diameter of the aperture stop S2 is limited so as to limit the aperture of the objective lens. At the high magnification end, the diameters of the aperture stops S1 and S2 are opened.
[0093]
As described above, in the fourth embodiment, as shown at (A) low magnification end, (B) intermediate magnification, and (C) high magnification end in FIG. 4, the second lens group G2 and the third lens group G3 are It is moving. This zooming changes the focal length from 45 mm (low magnification end) to 144 mm (intermediate magnification), and further from 360 mm (high magnification end). The number of fields of view at a focal length of 45 mm is 8, and at other focal lengths, the number of fields of view is 11.
[0094]
Further, the diameters of the aperture stops S1 and S2 are set so that the exit side numerical aperture is 0.03 when the focal length is from 45 mm to 144 mm. When the focal length is 144 mm to 360 mm, the aperture stops S1 and S2 are open. Thus, the pupil diameter of the objective lens is not limited by 14.4 mm by the aperture stops S1 and S2. As a result, the brightness of the image plane is kept constant at the low magnification end, and a decrease in the amount of light at the periphery can be suppressed.
[0095]
Further, in the fourth embodiment, the conditions (1) to (6) are satisfied despite the fact that the fourth embodiment is composed of a small number of lens groups including three lens groups. As a result, a zoom optical system having a high zoom ratio and excellent aberration performance has been realized.
[0096]
The optical system of the fourth example further satisfies the condition (8). Thus, the amount of movement of the second lens group G2 can be reduced, which is a preferable configuration in terms of layout.
[0097]
Although the configuration of the objective lens is not described in the fourth embodiment, the pupil diameter of the objective lens is 14.4 mm, and the distance from the pupil position of the objective lens to the first lens group is set to 121 mm. .
[0098]
The aberration states of the fourth embodiment are as shown in FIG. 17 (at a focal length of 45 mm), FIG. 18 (at a focal length of 144 mm), and FIG. 19 (at a focal length of 360 mm), respectively.
[0099]
The fifth embodiment of the present invention has a configuration as shown in FIG. In order from the rear of the objective lens, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G3 having a negative refractive power. It is composed of a lens group G4. Then, at the time of zooming from the low magnification end to the high magnification end, the second lens group G2, the third lens group G3, and the fourth lens group G4 move along the optical axis. At this time, the distance between the first lens group G1 and the second lens group G2 is reduced, the distance between the second lens group G2 and the third lens group G3 is increased, and the distance between the third lens group G3 and the fourth lens group G4. Becomes longer.
[0100]
In the fifth embodiment, the first lens group G1 is composed of a front lens group G1F composed of a convex lens, a cemented negative lens having a low power obtained by cementing a convex lens and a concave lens, and a rear lens group G1R composed of a positive lens. Have been. The second lens group G2 is composed of a cemented negative meniscus lens in which a negative meniscus lens and a positive meniscus lens are cemented. The third lens group G3 includes a cemented positive lens in which a negative meniscus lens and a convex lens are cemented, and a positive lens. Further, the fourth lens group G4 includes a negative meniscus lens having a concave surface facing the image surface side, a cemented negative lens having a biconcave lens having a strong concave surface facing the second lens group and a biconvex lens, and a convex lens. It is configured.
[0101]
Two aperture stops S1 (12 surfaces) and S2 (18 surfaces) are arranged in the optical system of the fifth embodiment. Since the pupil conjugate position of the objective lens is near the third lens group G3 at the low magnification end, the aperture stop S1 is arranged near the third lens group. At the intermediate magnification, the pupil conjugate position of the objective lens is located between the third lens group G and the fourth lens group. Therefore, the aperture stop S2 is disposed between the third lens group G3 and the fourth lens group G4. That is, at the low magnification end, the diameter of the aperture stop S1 is reduced so as to limit the aperture of the objective lens, and the diameter of the aperture stop S2 is opened. At an intermediate magnification, the diameter of the aperture stop S1 is opened, and the diameter of the aperture stop S2 is limited so as to limit the aperture of the objective lens. At the high magnification end, the diameters of the aperture stops S1 and S2 are opened.
[0102]
As described above, in the fifth embodiment, as shown at (A) low magnification end, (B) intermediate magnification, and (C) high magnification end in FIG. 5, the second lens group G2, the third lens group G3, The fourth lens group G4 is moved. This zooming changes the focal length from 45 mm (low magnification end) to 144 mm (intermediate magnification), and further from 360 mm (high magnification end). The number of fields of view at a focal length of 45 mm is 8, and at other focal lengths, the number of fields of view is 11.
[0103]
Further, the diameter of the aperture stops S1 and S2 is set so that the exit side numerical aperture is 0.032 when the focal length is from 45 mm to 144 mm. When the focal length is 144 mm to 360 mm, the aperture stops S1 and S2 are open. Thus, the pupil diameter of the objective lens is not limited by 14.4 mm by the aperture stops S1 and S2. As a result, the brightness of the image plane is kept constant at the low magnification end, and a decrease in the amount of light at the periphery can be suppressed.
[0104]
The fifth embodiment satisfies the conditions (1) to (7). This makes it possible to realize an optical system having a high zoom ratio and excellent aberration performance.
[0105]
In the fifth embodiment, the angle of incidence of the principal ray on the image plane is suppressed to about 2 degrees in any state of zooming by using four lens groups. That is, the configuration is effective in suppressing color shading, which is a phenomenon unique to CCD elements.
[0106]
Further, the fifth embodiment is configured so that the first lens unit satisfies the condition (8). Thus, the amount of movement of the second lens unit during zooming can be reduced, which is preferable from the viewpoint of layout. Although the configuration of the objective lens is not described, the pupil diameter of the objective lens is 14.4 mm, and the distance from the pupil position of the objective lens to the first lens group is set to 121 mm.
[0107]
The aberration states of the fifth embodiment are as shown in FIGS. 20 (at a focal length of 45 mm), FIG. 21 (at a focal length of 144 mm), and FIG. 22 (at a focal length of 360 mm), respectively.
[0108]
The sixth embodiment of the zoom optical system according to the present invention has a configuration as shown in FIG. In order from the rear of the objective lens, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a positive refractive power And a fourth lens group G4 having Then, at the time of zooming from the low magnification end to the high magnification end, the second lens group G2, the third lens group G3, and the fourth lens group G4 move along the optical axis. At this time, the distance between the first lens group G1 and the second lens group G2 becomes shorter, the distance between the second lens group G2 and the third lens group G3 becomes shorter and then longer, and the distance between the third lens group G3 and the fourth lens group G4 becomes shorter. The distance between the lens groups G4 becomes longer.
[0109]
In the sixth embodiment, the first lens group G1 is composed of a front lens group G1F including a convex lens, a cemented negative lens having a low power obtained by cementing the convex lens and the concave lens, and a rear lens group G1R including a positive lens. You. The second lens group G2 includes a cemented negative meniscus lens in which a negative meniscus lens and a positive meniscus lens are cemented. The third lens group G3 includes a cemented positive lens in which a negative meniscus lens and a convex lens are cemented, and a positive lens. Further, the fourth lens group G4 includes a negative meniscus lens having a concave surface facing the image surface side, a cemented negative lens in which a biconcave lens and a biconvex lens are cemented, and a convex lens.
[0110]
Two aperture stops S1 (12 surfaces) and S2 (18 surfaces) are arranged in the optical system of the sixth embodiment. Since the pupil conjugate position of the objective lens is near the third lens group G3 at the low magnification end, the aperture stop S1 is arranged near the third lens group. At the intermediate magnification, the pupil conjugate position of the objective lens is located between the third lens group G and the fourth lens group. Therefore, the aperture stop S2 is disposed between the third lens group G3 and the fourth lens group G4. That is, on the low magnification side, the diameter of the aperture stop S1 is reduced so as to limit the aperture of the objective lens, and the diameter of the aperture stop S2 is opened. At an intermediate magnification, the diameter of the aperture stop S1 is opened, and the diameter of the aperture stop S2 is limited so as to limit the aperture of the objective lens. At the high magnification end, the diameters of the aperture stops S1 and S2 are opened.
[0111]
As described above, in the sixth embodiment, as shown at (A) low magnification end, (B) intermediate magnification, and (C) high magnification end in FIG. 6, the second lens group G2, the third lens group G3, The fourth lens group G4 is moved. This zooming changes the focal length from 45 mm (low magnification end) to 144 mm (intermediate magnification), and further from 360 mm (high magnification end). The number of fields of view at a focal length of 45 mm is 8, and at other focal lengths, the number of fields of view is 11.
[0112]
Further, the diameter of the aperture stops S1 and S2 is set so that the exit side numerical aperture is 0.032 when the focal length is from 45 mm to 144 mm. When the focal length is 144 mm to 360 mm, the aperture stops S1 and S2 are open. Thus, the pupil diameter of the objective lens is not limited by 14.4 mm by the aperture stops S1 and S2. As a result, the brightness of the image plane is kept constant at the low magnification end, and a decrease in the amount of light at the periphery can be suppressed.
[0113]
The sixth embodiment satisfies the conditions (1) to (7), thereby realizing an optical system having a high zoom ratio and excellent aberration performance.
[0114]
In the sixth embodiment, the angle of incidence of the principal ray on the image plane is suppressed to about 2 degrees in any state of zooming by comprising four lens groups. That is, the configuration is effective in suppressing color shading, which is a phenomenon unique to CCD elements.
[0115]
Further, the sixth embodiment is configured so that the first lens group satisfies the condition (8). Thereby, the amount of movement of the second lens group can be reduced, which is preferable in terms of layout. Although the configuration of the objective lens is not described, the pupil diameter of the objective lens is 14.4 mm, and the distance from the pupil position of the objective lens to the first lens group of the zoom optical system is set to 121 mm.
[0116]
The aberration states of the sixth embodiment are as shown in FIG. 23 (for a focal length of 45 mm), FIG. 24 (for a focal length of 144 mm), and FIG. 25 (for a focal length of 360 mm).
[0117]
The seventh embodiment of the present invention has a configuration as shown in FIG. That is, in order from the rear of the objective lens, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a positive The fourth lens group G4 has a refractive power and the fifth lens group G5 has a negative refractive power. When the magnification is changed from the low magnification end to the high magnification end, the second lens group G2, the third lens group G3, and the fourth lens group G4 move along the optical axis. At this time, the distance between the first lens group G1 and the second lens group G2 is shortened, the distance between the second lens group G2 and the third lens group G3 is shortened once and then increased, and the distance between the third lens group G3 and the third lens group G3 is shortened. The distance between the fourth lens group G4 and the fourth lens group G4 becomes longer and shorter, and the distance between the fourth lens group G4 and the fifth lens group G5 becomes longer.
[0118]
In the seventh embodiment, the first lens group G1 is composed of a front lens group G1F composed of a convex lens, a cemented positive lens having low power in which the convex lens and the concave lens are cemented, and a rear lens group G1R composed of a positive lens. ing. The second lens group G2 includes a cemented meniscus lens of a negative meniscus lens and a positive meniscus lens. The third lens group G3 includes a cemented positive lens in which a negative meniscus lens and a convex lens are cemented. The fourth lens group G4 is composed of a positive meniscus lens and a cemented positive lens in which a negative meniscus lens and a convex lens are cemented. Further, the fifth lens group G5 includes a biconcave lens, a cemented negative meniscus lens in which the biconcave lens and the positive lens are cemented, and a positive meniscus lens.
[0119]
In the seventh embodiment, there is a position conjugate with the pupil position of the objective lens between the third lens group G3 and the fourth lens group G4. An aperture stop S is arranged near the pupil conjugate position. The aperture stop S moves on the optical axis integrally with the fourth lens group G4 during zooming.
[0120]
As described above, in the seventh embodiment, as shown at (A) low magnification end, (B) intermediate magnification, and (C) high magnification end in FIG. 7, the second lens group G2, the third lens group G3, The fourth lens group G4 is moved. This zooming changes the focal length from 45 mm (low magnification end) to 180 mm (intermediate magnification) and further from 900 mm (high magnification end). The number of fields of view at a focal length of 45 mm is 8, and at other focal lengths, the number of fields of view is 11. Also, the diameter of the aperture stop S is set so that the exit side numerical aperture is 0.032 when the focal length is from 45 mm to 180 mm. When the focal length is between 180 mm and 900 mm, the diameter of the aperture stop S is open. Thus, the pupil diameter of 17.09 mm of the objective lens is not limited by the aperture stop. As a result, the brightness of the image plane is kept constant at the low magnification end, and a decrease in the amount of light at the periphery can be suppressed.
[0121]
In the seventh embodiment, since the amount of movement of the third lens unit is small, the incident angle of the principal ray on the image plane I is suppressed to about 2 degrees in any state during zooming. That is, the configuration is effective in suppressing color shading, which is a phenomenon unique to CCD elements.
[0122]
Although the configuration of the objective lens is not described in the seventh embodiment, the pupil diameter of the objective lens is 17.09 mm, and the distance from the pupil position of the objective lens to the first lens group G1 is 171 mm.
[0123]
The aberration states of the seventh embodiment are as shown in FIGS. 26 (at a focal length of 45 mm), FIG. 27 (at a focal length of 180 mm), and FIG. 28 (at a focal length of 900 mm), respectively.
[0124]
In the aberration diagrams of each embodiment, FIY is an image height.
[0125]
The zoom optical systems according to Embodiments 1, 2, 3, and 7 of the present invention described above can be used in combination with, for example, an objective lens having a magnification of 20 times, a focal length of 9 mm, and a numerical aperture of 0.9. In this case, at the low magnification end, the total magnification is 5 and the numerical aperture is 0.16. At the high magnification end, the total magnification is 100 times and the numerical aperture is 0.9. In this manner, observation and photographing can be performed with a total magnification of 5 to 100 times and a numerical aperture of 0.16 to 0.9.
[0126]
In addition, at the low magnification end, blurring due to the aperture stop S can be suppressed, so that aberration performance can be improved. Further, since the configuration is such that the angle of the principal ray incident on the imaging surface is 2 degrees or less, shading does not occur in an imaging device such as a CCD device, and good imaging is possible.
[0127]
The zoom photographing optical system according to the present invention is as described in detail above, and in addition to the configuration described in each claim, the one described in each of the following claims can also achieve the object of the present invention.
[0128]
[1] In the optical system according to claim 3, the first lens group includes a plurality of lens components including at least a cemented lens including a positive lens and a negative lens, and is closest to the final image. A zoom photographing optical system that includes at least one lens having a negative refractive power whose concave surface faces the intermediate image side in the lens group, and satisfies the following conditions (6) and (7).
(6) νP−νN ≧ 30
(7) Gn ≧ 1.6
However,
νP is the Abbe number of the positive lens of the cemented lens in the first lens group,
νN is the Abbe number of the negative lens of the cemented lens in the first lens group,
Gn is the refractive index of the lens having a negative refractive power with the concave surface facing the intermediate image side.
[0129]
[2] The optical system according to [1], wherein the first lens group includes a front group and a rear group, and satisfies the following condition (8).
(8) 0.3 <D11 / D1 <0.8
Here, D11 is an interval between the front group and the rear group.
[0130]
[3] A zoom photographing optical system according to claim 1, wherein a fourth lens unit having a negative refractive power is arranged on the image side of the third lens unit having the positive refractive power.
[0131]
[4] A zoom photographing optical system according to claim 1, wherein a fourth lens unit having a positive refractive power is arranged on the image side of the third lens unit having a positive refractive power.
[0132]
[5] The optical system according to claim 1, wherein the fourth lens unit having a positive refractive power and the fourth lens unit having a positive refractive power are located on the image side of the third lens unit having the positive refractive power. A zoom photographing optical system in which a fifth lens unit having a refractive power is arranged.
[0133]
[6] The optical system according to claim 1, wherein the fourth lens unit having a positive refractive power and the negative lens unit are disposed on the image side of the third lens unit having the positive refractive power from the objective lens side. Zoom photographing optical system with fifth lens group with refractive power
[0134]
【The invention's effect】
The zoom photographing optical system of the present invention forms an object image by an objective lens of a microscope on an image sensor, has a high zoom ratio of 20 times while maintaining high optical performance, and improves operability and systematility. It has effects such as gain.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of a second exemplary embodiment of the present invention.
FIG. 3 is a diagram showing a configuration of a third exemplary embodiment of the present invention.
FIG. 4 is a diagram showing a configuration of a fourth embodiment of the present invention.
FIG. 5 is a diagram showing a configuration of a fifth embodiment of the present invention.
FIG. 6 is a diagram showing a configuration of a sixth embodiment of the present invention.
FIG. 7 is a diagram showing a configuration of a seventh embodiment of the present invention.
FIG. 8 is an aberration curve diagram of the first embodiment at a focal length of 45 mm.
FIG. 9 is an aberration curve diagram at a focal length of 180 mm in the first embodiment.
FIG. 10 is an aberration curve diagram of the first embodiment at a focal length of 900 mm.
FIG. 11 is an aberration curve diagram at a focal length of 45 mm in the second embodiment.
FIG. 12 is an aberration curve diagram of the second embodiment at a focal length of 180 mm.
FIG. 13 is an aberration curve diagram at a focal length of 900 mm in the second embodiment.
FIG. 14 is an aberration curve diagram at a focal length of 45 mm according to the third embodiment.
FIG. 15 is an aberration curve diagram of the third embodiment at a focal length of 180 mm.
FIG. 16 is an aberration curve diagram at the focal length of 900 mm in the third embodiment.
FIG. 17 is an aberration curve diagram at the focal length of 45 mm in the fourth embodiment.
FIG. 18 is an aberration curve diagram at the focal length of 144 mm in the fourth embodiment.
FIG. 19 is an aberration curve diagram at a focal length of 360 mm in the fourth embodiment.
FIG. 20 is an aberration curve diagram at a focal length of 45 mm according to the fifth embodiment.
FIG. 21 is an aberration curve diagram at the focal length of 144 mm in the fifth embodiment.
FIG. 22 is an aberration curve diagram at a focal length of 360 mm in the fifth embodiment.
FIG. 23 is an aberration curve diagram at a focal length of 45 mm in the sixth embodiment.
FIG. 24 is an aberration curve diagram at a focal length of 144 mm in the sixth embodiment.
FIG. 25 is an aberration curve diagram at a focal length of 360 mm in the sixth embodiment.
FIG. 26 is an aberration curve diagram at a focal length of 45 mm in the seventh embodiment.
FIG. 27 is an aberration curve diagram at a focal length of 180 mm in the seventh embodiment.
FIG. 28 is an aberration curve diagram at a focal length of 900 mm in the seventh embodiment.

Claims (3)

An optical system for forming a final image of a sample, which is used in an optical device having an objective lens, and includes, in order from the objective lens, a first lens group having a positive refractive power and a second lens group having a negative refractive power And at least a third lens unit having a positive refractive power, and at the time of zooming from the low magnification end to the high magnification end, the distance between the first lens unit and the second lens unit is shorter at the high magnification end than at the low magnification end. The second lens group and the third lens group move along the optical axis, respectively, such that the distance between the second lens group and the third lens group is longer at the high magnification end than at the low magnification end. A zoom photographing optical system in which an intermediate image is formed between the first lens group and the second lens group at an end, and the following conditions (1) and (2) are satisfied.
(1) 1 ≦ FH / FL ≦ 3
(2) 3 ≦ MGH / MGL ≦ 20
However,
FH is the focal length of the entire lens group between the first lens group and the intermediate image position at the high magnification end,
FL is the focal length of the entire lens group between the first lens group and the intermediate image position at the low magnification end;
MGH is the magnification of the entire lens group between the intermediate image position at the high magnification end and the final image position,
MGL is the magnification of the entire lens group between the intermediate image position and the final image position at the low magnification end. The zoom photographing optical system according to claim 1, wherein the following conditions (3), (4), and (5) are satisfied.
(3) 0.3 <D1 / D0 <0.7
(4) 0.15 <D2 / D0 <0.7
(5) 0 <FB / D0 <0.3
However,
D0 is the distance from the lens surface closest to the objective lens in the first lens group to the final image position;
D1 is the distance at the low magnification end from the lens surface closest to the objective lens in the first lens group to the intermediate image position;
D2 is the amount of movement of the second lens group when zooming from the low magnification end to the high magnification end,
FB is the distance from the lens surface on the final image side of the lens closest to the final image to the final image. The conjugate image of the pupil of the objective lens is formed between the intermediate image and the final image, an aperture stop is arranged at the position of the conjugate image, and the diameter of the aperture stop is changed. 2 zoom optical system.

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